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UG
/5"3
FKOFESaOHAL PATERS OF THE CORPS OF ENfflNEERS. U. S. ARHT
No. S9
ENGINEER FIELD MANUAL
j PARTS I-VII
1. RECONNAISSANCE
H. BRIDGES
in. ROADS
IV. RAILROADS
V. FIELD FORTinCATION
VI. ANIMAL TRANSPORTATION
VIL TABLES. WEIGHTS. MEASURES, AND
SPECIFIC GRAVITIES
HFTH (REVISED) EDITION
WAR DEPARTMENT.
Docmnent No. 355.
Office of the Chief of Engineers,
1 '*
<^
Ne
War Dbpartmbnt,
Office of the Chief of Staff,
Washington, November 19, 1909,
The Engineer Field Manual, United .States Army, prepared under
the direction of the Chief of Engineers, United States Army, is
published for the information and guidance of all concerned ; it will
not be modified except by specific authority given in each case.
Any changes or suggestions that may occur to officers or others
using the manual will be submitted to the Chief of Engineers for
consideration in connection with the publication of future editions.
By order of the Secretary of War :
J. Franklin Bell,
Major General, Chief of Staff.
313618
War Department,
Office of thd Chief of Engineers,
Washington, Maroh 12, 1907.
The Adjutant General.
Sir : 1. By authority of the Secretary of War, six parts of the
Engineer Field Manual, compiled under the direction of this oflftce
by Lieut. Col. Smith S. Leach, Corps of Engineers and General StaflT,
have been published in five separate volumes. These parts are :
Part I, Reconnaissance; Part II, Bridges ; Part III, Roads; Part IV,
Railroads, and Part V, Field Fortification (in one volume) ; and
Part VI, Animal Transportation. Each of these six parts received
the approval of the Chief of Staff before its publication.
2. It is now desired to publish under a single cover these six
parts, revised and corrected, for issue to the service when ready for
distribution.
3. In addition to the correction of such Qfrors as have been dis-
covered in the original editions it is proposed to add some new matter
to bring the work up to date. The most important addition is a
description of the new types of instruments adopted in 1906. It is
also desired to add, in Part I, a brief description of the new military
survev of Cuba ; some additional topographical signs and symbols
recently prescribed by the General Staff, and a brief account of the
new system of angular measurement in mils adopted for position
finding by the Field Artillery ; to Incorporate, in Part II, a very
useful table of dimensions of floor systems for stated loads and
spans, and to incorporate, in Part V, a plate and description of the
Fort UUey redoubt, which presents several excellent features of
design. It is proposed to add the new matter at convenient places
as nearly . in its topical relation as possible, but under a caption
"Addenda, 1907."
4. The mechanical work involved in the preparation and publica-
tion of this revised edition would be, roughly, as follows : Drawing
and engraving of four or five plates ; making of a consolidated index ;
composition of the equivalent of about three or four pages of text ;
composition of consolidated index (about 48 pages) ; electrotyping
of new plates, new pages of text, and new index ; repaglng of Parts
II to VI, both inclusive, and printing and binding of 1,000 copies
of the complete work, the cover to have a pocket, a pencil tube, and
a broad fiap folding over the back. The manuscript of a proposed
introduction and list of authorities is inclosed.
5. The matter in the six parts as now published is electrotyped ;
the electrotype plates are at the Government Printing Office. The
expense of drawing and engraving the new plates, of preparing the
new matter, and of making the consolidated index would be charge-
able to the appropriation carried by the Army appropriation act
approved June 12, 1906, *' For pontoon material, tools, instruments,
and supplies required for use in the engineer equipment of troops,
including the purchase and preparation of engineer manuals," of
which there is an available balance sufficient for the purpose ; the
expense of composition, electrotyping, repaglng existing electrotype
plates, and of printing and binding to be borne by the appropriation
for public printing and binding. The paper for the work is on hand
in tnis office.
6. I have the honor to recommend that 1,000 copies of the revised
edition of the six parts of the Engineer Field Manual, as hereinbefore
described, and their accompanying plates be printed at the Govern-
ment Printing Office and furnished for the use of this office on the
usual requisition, the cost to be paid as stated in the preceding
paragraph.
7. A copy of each of the parts as published is submitted herewith.
Very respectfully,
A. Mackeneib,
Brig, Cfen,, Chief of Engineers, U, 8^ Army,
4
ENGINEER FIELD MANUAL.
INTRODUCTION.
In April, 1899, the Chief of Engineers directed the commandant of
the Engineer School to enter upon the preparation of an Engineer
Field Manual. At the same time all officers of the Engineer Corps
who had been in the field during the Spanish War were invited to
contribute data and suggestions, and many of them did so. At the
Engineer School the work of compilation was committed to the
Instructor in civil engineering, then Capt. Henry Jervey, and under
bis control, and mostly by his own hand, a general plan of a manual
was worked out, manuscript and plates prepared on the subjects of
reconnaissance and bridges, and more or less complete notes on roads
and railroads.
The instructions of the Chief of Engineers required a topical
division and publication by parts, as completed. The part on recon-
naissance was published in tentative form and distributed to officers
of Engineers and other arms and to a few civil engineers, for com-
ment and criticism. The parts on bridges and roads were sent in
manuscript to certain Engineer officers for like criticism. As a
result, the method of treatment of subject-matter and the mechanical
features of the book were definitely determined and it was decided
to revise the work already done to conform it to the modified plan
and to republish Part I.
At this stage, 1903, the pressure of work at the Engineer School
made it necessary to plaice this duty in other hands and it was de-
volved upon the commanding officer of the First Battalion of Engi-
neers, and shortly thereafter the relation of that officer to the
preparation of the manual was made personal, instead of ex officio,
and all subsequent work has been by the same hand.
By July 1, 1906, six parts had been published — reconnaissance,
bridges, roads, railroads, field fortification, and animal transporta-
tion. These parts are now collected in a single cover, with correc-
tions of errors which crept into the first edition and some additions
of new matter which has become available since the first publication.
The most important of these additioms, made by direction, of the
Chief of Staff, is the incorporation of the signs, etc., for finished
maps, published by authority of the Secretary of War in 1904. A
few minor changes which have been approved will be noted.
The opportunitv now first offers to make acknowledgement of
sources from which m^tfrlaJL has beon drawn and of assistance
rendered by persons in the preparation and publication of the
manual.
As to authorities, a list is appended o£ works whiph Tmyq been
consulted and from which facts or suggestions have beed derived.
Other works have been con»ilted, but nothing having oeen taken
from or suggested by them, they are not mentioned. The titles in
the list which appear in full-face type have been relied upon* move
or less, as standard and as guides to topics and arrangement. But
a single work seems to deserve further mention, and that Is the
6 EN6INEEB FIELD MANUAL.
incomparable Trantwine, the indebtedness to which is too obvious
to require mention, but too important to permit it to be dispensed
with. Substantially no matter from any source is quoted. The
exigency of space required everything used to be rewritten with a
view to condensation. In addition to the works cited, much valu-
able information, especially as to railroads and field fortifications,
was obtained from the reports of military observers with the Japa-
pese and Russian Armies and from fugitive publications as to the
war in Manchuria. Of the latter, the Journal of the Royal Engi-
neers of Great Britain deserves special mention.
Personal assistance in the preparation of text has come exclusively
from brother ofilcers of the Corps of Engineers, with the single ex-
ception of " Landscape sketching," paragraph 85, and plates 39 and
40, '• Reconnaissance," which was abstracted from material fur-
nished by Prof. C. W. Larned of the Military Academy. In verifying,
criticizing, and correcting the work of the compiler, many officers
have rendered assistance in greater or less degree, and none who
have had opportunity to assist have refused. But a few have given
60 much of time ana labor as to make mention by name an act of
simple justice. Lieut. Col. Abbot, who has handled the manual In
the office of the Chief of Engineers during the entire period of
preparation and publication, has contributed never-falling enthusi-
asm, encouragement, and counsel, which have been of the greatest
possible assistance. MaJ. Rees read critically the parts on recon-
naissance, bridges, and roads. Maj. Sibert and Lieuts. Johnston and
Spalding did the same for railroads. Capt. Connor read the same
part and forwarded a paper of his own on the subject, from which
some suggestions were taken. Maj. Gaillard read the parts on field
fortification and animal transportation and made valuable suggest
tions from personal experience with pack trains. Capt. Cheney
read the part on animal transportation and made valuable sugges-
tions. This part was also read by Dr. Hunter, V. S., Sixth Cavalry,
and Mr. Daly, chief packer, upon whose approval much of its value
rests. The original drawings for Parts I and II were made by en-
listed men of the Second Battalion of Engineers, under the super-
vision of Maj. Judson, instructor of military engineering at the
Engineer School. The names of these men unfortunately nave not
been made of record. These drawings were revised and those for
Parts III and VI made by Sergt. Pihlgrem, of the First Battalion of
Engineers, assisted for a short time by Corp. Plugel of the same or-
ganization. The drawings for Parts IV and V and the Addenda
were made by Mr. S. P. Hollingsworth, of Washington, D. C. The
indexing, partial and consolidated, was done by Mr. G. T. Ritchie of
the Library of Congress. Mr. Pickering Dodge, chief clerk. United
States Engineer Office, Washington, D. C, contributed valuable
assistance in final proof reading.
LIST OF BOOKS CONSULTED.
Theory and Practice of Surveying. Johnson.
Mtlttary Topogrrapliy and Slcetcliti&gr* Root.
Tables and Formnlfe. Lee.
Higher Surveying. Gillespie.
Roads and Railroads. Gillespie.
Enstneer'0 Poclcetboolc. Trautwine.
V. S. Bridge Eqntpaare and Ponton Drill.
Military Bridges. Haupt.
Roads and Pavements. Baker.
Masonry Constrnctton. Baker.
Highway Construction. Byrne.
Economic Railroad Location. Wellington.
Railroad Constrnctton. Webb.
Hotes on Trade Camp.
Railroad Curves. Allen.
UTTEOBTFCTIOH. 7
The Railroad Spiral. Searles.
The Roadm»«ter's Assistant. Railroad Gaiette.
LoeomottTe Brealcdo^vns. Smersenctes, and their Rem-
edtes. Fowler.
Text-book on Locomotives. Intematioiial Correspondence Schools.
Train Rules and Train Dlspatclilns* Dalby.
Block Signal Operation. Derr.
Letters of an Old Railway Official. Hine.
Manual of Field Enarlneerlnflr* Beach.
F*leld Fortification. Fiebeger.
Manual of Military Bnslneerlns* Ernst.
Attack of Fortified Places. Mercur.
Royal Engineers Aide Memoire.
Handbook of Modern Explosives. Eissler.
Woolwich Text-book, Parts I and II.
Chatham Text-book, Parts II and III.
Text-boolc of Field Snarlneerlns* Phillips.
Field Fortification. Hutchinson.
British Manual of Field Engineering. 1903.
Destruction of Obstacles in Campaign. Bornecque, Tr. Burr.
V. S. Field Service Resnlatlons.
Manual of the Quartermaster's Department, U. S. Army.
Horses, Saddles, and Bridles. Carter.
Packer's Manual. Daly.
Treatise on Feeding and Training of Mules. Riley.
Military Transport. Furse.
PART I.
RECONNAISSANCE.
PART I— RECONNAISSANCE.
1. TopoflTvaplifcal reconitaissance, as here treated, coren the
Instruments and methods necessary for the production of maps of
SMALiLi AREAS and routes of travel of sufflcient accuracy for tem-
porary military needs.
No reconnaissance sketch or combination of sketches can be expected
to cover with sufficient accuracy an area of more than about 2 miles
on a side. Areas up to 10 miles on a side can be satisfactorily
mapped for military purposes by running transit or plane table con-
trol traverse lines which will locate some landmark in each square
mile, adjusting the traverses, plotting the adjusted traverses, and
then filling in the control skeleton thus obtained by sketching.
For larger areas triangulatlon or traverse control of greater ac-
curacy is necessary and the curvature of the earth soon becomes a
factor. No map of an area over 10 miles on a side should be under-
taken without a thorough knowledge of the best modem practice in
topographic mapping such as that followed by the United States
Geological Survey.
2. The information to be obtained in a topographical roconnaissance
may be grouped under the headings of ttmey cover, resources, and
BonteBclature. The map should permit a determination of the
time which a column will require to pass between any two given
points by showing the distance between them and the condition of
the road or country which must be traversed, as regards its effect on
the rate of march ; the accidents of ground which will afford cover
to the army or to the enemy ; the location, quantity, and quality of
water, fuel, grass, etc., and should give to each feature its local name.
The last requirement is of great importance and Is the one most often
I neelected.
3. Tlfte fvndamental topoirraplilcal operation Is the deter-
mination of the direction and distance of one point from another
point.
The direction of one point from another is composed of two ele-
ments : First, the angle made by the line joining the two points, with
a vertical plane passing throii^h one of them. This angle is measured
in a horizontal plane and is called the aaiBi«tli| second, the angle
made by the line joining the two points, with a horizontal plane pass-
ing through one of them. This angle is measured in a vertical plane
passing through both points, and for convenience will be callea the
multeiat.
4. AslntvtliSv-^As an infinite number of vertical planes may pass
throogh a given point, it Is necessary to select one as the origin of
ailmoths. In topographical reconnaissance the plane selected is that
of the magnetic meridian at the point. Its direction in a horizontal
plane is the line of rest of a freely suspended and balanced magnetic
needle, and this line is the origin of asimuths.
Prom this origin azimuths are measured In degrees of arc from O
to 860, passing from the north point through the east, south, and
west to north again. Azimuths of 0* to 90** are in the northeast or
11
18 ENOINEEB FIELD XANTTAL.
first quadrant (fig. 1) ; those of 90*" to 180^ are in the southeast or
second quadrant ; those from 180® to 270** in the southwest or
third quadrant, and those from 270® to 360® in the northwest or
fourth quadrant.
Azimuths are bearings between stations taken in the direction of
progress of the reconnaissance. Bearings taken in the other direc-
tion are called back azlmntfeis. If the stations are numbered in
the order they are occupied, a bearing from a lower to a higher
numbered station is an azimuth, and a bearing from a higher to a
lower number^ station is a back azimuth.
The method of stating azimuths described above is that commonly
used in surveying when direction is maintained by carrylnflr an
aslmiitlK. It is the simplest to understand and use, and permits the
angle between any two lines to be read at a glance.
There are other ways of expressing azimuths, adapted to special
conditions or circumstances. In astronomical work and tables the
azimuth is reckoned frcmi the sontb, through W., N., and £., 360® to
south again. Any astronomical azimuth difiters from the corre-
sponding survey azimuth by 180®.
In navigation azimuths are reckoned from the laariner's com-
pass, and are called bearinss* The dial is divided into 32
points and each point into Qvarter points. The names of the
points and their relation to survey azimuths are shown in figure 1.
Land surveyors reckon bearings in both directions from N. and S.
Their compasses are graduated 90® in each direction from the N.
and S. points and a bearing is stated by giving the angle and
direction from N. or S., whichever may be nearest, as N. 46® W., S.
29® B.
Formerly such bearings were reckoned from the nearest cardinal
point, N., S., E., or W., as W. 40° N.. which corresponds to N. 46®
W. This method Is very convenient for giving directions in orders
and reports. It is shown in the middle circle of figure 1.
5. A special method of azimuth measurement has been adopted for
use In the fire control of field artillery. The unit, called a mil, is the
arc whose length is one one-thousandth of the radius. By computa-
tion this arc is 3'. 437 + . This length is not commensurate with the
length of the circle being ^contained in it 6,283.24 times. For con-
venience of graduation, the circle is divided into 6,400 equal parts,
assumed to be mils, the angular value of each of which is 3'.375,
differing from the computed value by nearly 2 per cent, which error
enters into all determinations and is neglected.
Each change of 1 mil in azimuth corresponds to a change in posi-
tion in a direction perpendicular to the line of sight of one one-
thousandth of the range. This method reduces all elements of fire
control to functions of the range.
6. The compass is the standard instrument for the determination
of azimuths in topographical reconnaissance. It consists of case,
needle, card, piVQt, and atop, figures 2 and 3.
The card mav be Ax«d to the case or movable, attached to the
needle and revolving with it. The stop raises the needle from the
givot and clamps it against the glass cover. A good compass must
ave a needle sufficiently magnetized to settle accurately and a pivot
free from rust and roughness. If the needle becomes too weak, it may
be remagnetized by rubbing gently from pivot to point on a perma-
nent or electro magnet, each end of the needle to be rubbed on the
pole which attracts it In returning the needle for another stroke
carry it a foot or more from the magnet. The pivot may be poiished
with Putz pomade or similar substances on a soft stiek.
If possible, however, turn in the defective compass and get a good
one in place of it.
A needle loses part of its magnetism if kept for a long time oat ol
the plane of t^e magnetic meridian. In storing a comnass earc
should be taken to place it in the case or on the shelf with the N.
end of its needle pointing nbrth.
mKcomiTAisaAirci.
14 ENQINEXK PIZXI) MASVAL.
7. Dip. — ^The earth's magnetic poles are beneath the surface, and
the end of a symmetrical needle is drawn downward out of the hori-
zontal plane so as to point to the nearest pole. This displacement
from the horizontal plane ia called dip, and is measured in degrees of
arc. The dip increases generally with the latitude. Immediatelv
over a magnetic pole the needle stands vertical or has a dip of 90 .
Near the equator, where north and south poles exert an equal
influence, the needle may be horizontal or the dip 0.
For reading azimuths the needle must be kept in a horizontal plane,
which is done by a small movable counterweight. For considerable
changes in latitude, as in passing from the United States to the
Philippine Islands, the counterweight will require adjustment to
keep the needle horizontal, and in passing from the northern to the
southern hemisphere the counterweight must be changed to the
opposite side of the pivot.
There are t-wo adopted forms of compass for topographical
reconnaissance, one of the fixed and one of the movable card type.
The box compass is shown in figure 2. The card is fixed and
graduated counterclockwise from N. 360° to N. again. The E. and
W. points, if marked, are reversed. The stop is operated by opening
and closing the lid. The lid is liinged parallel to toe north and soutfi
line, and when open its upper edge forms a convenient line of sight.
The needle when stationary can be read to the nearest degree by the
eye, and to half a degree with a reading glass.
Another pattern wnich has been issuedf has the lid on an E. and
W. side, and the sighting line is a fine line drawn across the lid.
Some of the box compasses in use are graduated clochrwlse. Care
must be taken in using these. The true azimuth is 360** mlnns the
reading of the needle. The actual reading of such a compass should
never be recorded ; the corresponding azimuth only should be set
down. It will be safer to add a rough graduation in the proper
direction.
8. The prismatic compass is shown in figure 3. It is of the
movable-card type. It is read through a reflecting inverting magni-
fying prism. The prism revolves on an axis and is over the circum-
ference of the card for reading and against the edge of the case for
carrying. If, when so adjusted, the scale is out of focus when the
sight is taken, it shows that the card is not horizontal, and the case
must be tilted until the scale comes into focus. The needle may be
compensated for dip by a bit of sealing wax stuck on the underside
of tne card. The leaf sight folds down for carrying, and in so doing
stops the needle.
In this pattern, the metal cover has a window in it opposite the
prism, and is not removed when sighting. The leaf sight folds down
outside the cover and is not protected.
9. Compass errors. — The magnetic and true meridians generally
do not coincide. The angle which the needle makes with the true
north. at any place is called the declination of tlie needle, or
magnetic declination at that place. For latitudes of 60*" and less
the declination ordinarily varies between limits of 20** east and 20**
west. For high latitudes the declination is greater and more irregular.
There are daily and secular variations of declination at ev^ry place,
but they are too small to have any bearing on the class of work novr
under consideration, and for purposes of topographical reconnaissance
the declination at any place may be considered constant for the period
of the survey.
A close watch must be kept for the change in declination from place
to place and for local disturbances of the needle due to the proximity
of magnetized substances, natural or artificial.
Change of declination or normal direction of the needle should be
checked frequently. If a change is observed, it is certain to have taken
place gradually, and. If desired, may be distributed among the courses
run. though the change will seldom be great enough in a single day*a
work to make its distribution practicable.
Abnormal deflections of tbe needle, due to local disturbances,
are sudden and erratic and should not be distributed among all the
courses, but only among those in wlxtch there is reason to beliere the
disturbance occurs.
A simple way to detect — not measure — such disturbances is to take
freguent back azimuths. If the position of the needle is normal at
t)oto stations, the azimuths and back azimuth will differ by 180**. If
there is local attraction on the course, it will usually be stronger or
cause a greater deflection at one station than at the other, and the
azimuth and back azimuth will not differ by 180 **.
Another way is, when taking the bearing to a station, to select a
well-defined point beyond and on the same course. On arriving at the
Dew station, take a bearing from there to the selected point ahead.
If it is- the same as the first bearing to that point, there probably is
00 local disturbance. If the two bearings to the same point differ,
there probably is local disturbance.
A course in which local attraction is detected or suspected should
be noted, and if, on closing, an azimuth correction Is necessary, it
should be applied to the suspected courses.
10. Gradients. — ^There can be but one horizontal plane through a
given point, and it may be determined by the spirit level or plumb line
without serious error. Gradients are measured by taking the angle of
the line of direction with a horizontal line through the point.
11. Gradients are commonly called grades or slopes and are ex-
pressed in degrees, as 1°, 2**, 31**, QV slope, etc.
Each angle corresponds to two slopes, one up and one down from
the initial point. Rising grades may be recorded with a + before, or
an R after the number of degrees ; lalling grades with — before, or F
after. On a map, general slopes are indicated by an arrow pointing in
the direction of the drainage, with the gradient written beside it,
thus 3 >. Road grades are indicated by an arrowhead at
top and bottom of the grade, the one at top pointing toward the road
and the one at bottom away from It, thus i g •
Gradients are also expressed by tbe relation between the change of
elevation— rise or fall — ^and the corresponding horizontal distance.
This relation is stated in various ways.
By the rise in feet per 100 feet horizon or the foot rise as a per-
centage, as '• the slope Is 4 in 100, or 4 per cent."
By the foot rise for 1 mile of horizontal distance ; as ** the grade
is 50 feet,'* or "a 50-foot grade." This method and the preceding
are commonly used for railroad track grades.
By the number of feet horizontal corresponding to 1 foot rise; as
?' to 1, 10 to 1. This method is commonly us^^ for slopes of em-
bankments and excavations when less than 45°.
By the foot rise corresponding to 1 foot horizontal ; as, 1 on 1.
6 on 1 . This method is commonly used for slopes of embankments
and excavations, etc., from 45° to 75**.
By the number of inches horizontal corresponding to 1 foot rise ;
a«^ 3 inches to the foot, 1 inch in the foot. This method is com-
monly used for gradients of 70** and over and is called hatter.
TABUt L
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1
1-3
1.7
2.1
2.7
3.7
5l7
&S
7.1
)»wl
9-5
11.4
13
14
16
1?
23
29
33
3S
46
57
76
115
I
i
I
13. Tbe cIlBometer 1b the Instrument adopted for meaxudng
giadlents. vltb the horizontal plane Indicated b; «. spirit level. It
coDBiBtB {flg. 4) of H sight tabe. A, with a gradudted vertical arc, B,
Cuteued to It, and a level tube, C, with attached Indei arm. O,
revolving about o horlaontal ails through Ihe center ot the vertical
aim. The base ol tbe glght tube U a plans parallel to tbe Hoe ot
Bigbt. Under tbe center ot tbe level tube Is an opening in tbe sight
tube, inside of wblcb Is a mirror occupying one-half tbe width ot
the Bleht tube and facing tbe tye end at an angle of *5' wltb tbe
line of Bight. A horliontal wire ertenda across tbe middle of the
algbt tnbe in front of the mirror. When the babble Is brought to
tbe center, ItB rcficcted image seen from tbe eye end apiieare to be
bisected by the wire.
The central position of tbe bubble Indicates that the level tube Is
horizontal, and the reading of the Index arm upon tbe arc Is the
aogle betweea the axis of the level tube and tbe line of nlgbt. This
reading should be 0° when these lines are parallel. The vertical arc
is graduated each waj from 0° at Its middle point. Tbe Index arm
haB a double vernier wboee amallest rending Is 10' of an'. Gmdlenta
of more tban 45° are difficult to measure on acconnt ot the fore-
Btortenlug of the level tube as reflected In the mirror.
When ^e vernier Is Bet at 0°. the Inatrumenl ma; be nsed (S a
hand level ta locate points at tbe same elevation as tbe eie. Tbe
graduation on the Inner edge of the vertical limb corresponils to the
ordinary fractional method ol Indicating slopes, as 1 on :i, 1 on 10.
etc. This Bcale Rhould be read on the forward edge of tbe Index
arm, or in some forms on a special Index mark on a shorter part of
the arm.
The level tube la na4« parallel to (he al«bt take by the
adjusting BcrewB B (flg. 4), To test and correct the adjnstment.
place the Inetrument on a smootb surface, tbe more nearly horizontal
tbe better, and mark carefully tbe position of one side and one end
of the sight tube. Center tbe bubble by moving the ludax arm, and
read tbe vernier. Keverse tbe Instrument, bringing the other side
and end of the sight tube to the marks. Center tbe bubble by
moving the Index arm, and read again. Note and record Cor each
reading Its direction from 0°. wbettrer towr— ■ — * -"-e eye
end ot tbe sight tube. Note and record ell e eye
end Id each position with respect to some fl I* lo-
If the f
. - , - ^ . Place
tbe first poBltlon and ) the
f the adjusting screws . t tbe
"" "" e?pondlog to the second reading and
place tbe Instrument In tbe Becond position. Ttie bubble slioold
come to tbe middle.
Tbe STsvltr cllnonaetep adopted In 190B Is shown In Sgure S.
(rolled by a pendulum. Tbe Hue of Bigbt la throueh the peep L and
a glass-covered opening at M. Tbe lero line Is engraved on the glass.
A mirror near tbe center refiects tbe scale back to tbe peep. Looking
througb the iDstrntaent tbe object Is seen on tbe zero line, and at
one end of the latter a graduation of the scale la visible. The gradn-
tttons are from zero at the borliiontal each way to 45° tbe gradua-
Uons and numbers for elevation being In red and those tor depresalon
m black.
A sliding bar at B unlocks the spring-controlled stop, which, when
pressed, frees the pendulum and graduated circle, sad when released
g line or sight ott'object and read.
EIIQINES2 TULD KAKUAL.
rcLJ
BBconruBSAiroE. u
A typo ot hand level deBlgnrd tor slope readings Is now gen-
eralJy preferred to the ellnometer. This hand level ba* boitaoDtsl
lines OD the object slasi, eltber rradtne degrees or pet cent. With
the per cent ccadiuiUonB It U possible to obtain dlffereoces of eleya-
tlOD without Ihe uecessit; of using tables of degrcEs for dllTereaces
mlted for use with the ez-
■ hy the plnmb line !■
lan with the clinometer,
" ". line of Bight be
board Bud is readll; Im-
b; sweeping an arc of a
le IntersectloD of Ibe per-
the perpeudlcular at D
a lenyth to the radlDS CD
1 radius of 0.T8 Inches, or
^ iDCh, or a radius of TA
ordln^y as the scale used
the chorda form a gradn-
wn OD the lower e&e of
IS Indicated In the ncure.
qalckt; tilted so that the
H then turned to a horl-
llng taken ; or, whCE' the
d lata nee Che elevation of
nee may be derived. The
:h 1b known by comparing
The plane of reference Is taken low enough ho that no point of the
area to be covered hv the reconnaissance will be below it. This makes
all elevations positive. Knowing tbe helglit of a point almve this
Clans of reference, the elevation of any other point may be obtnlned
T taking the gradient and distance (o that point, deriving from
Ihem the dtOlerence of height between the two points, and adding thla
difference to the elerntlnn of the flrxt point If tbe gradient Is rising,
or aubtractlng It If the gradient la falling.
The elevation for a given gradient and dlatnnce depends apon
whether the distance Is measured aluni; the graiUcnt or along the
kartaontat. Distances paced are along the gradient. Those measured
■Itb a chain will also usually be on the slope, tliougb sometlmi'B care
i> taken to hold the chain horizontal, In which case the table for
horizontal distances Is to be used. Those dclcrmlued by Interaectlona
or acaled from a map are along the horizontal.
The differences of elevation corresponding to various gradients and
any dltrtancea may he taken from the following tablet :
xxaiasKB. nxLS mamual.
borlionUt disIsDces.
The difference of pIi-tsIIod fnr onj/ (n^dienl and _..„
Cum ma; be obtained b; maltlpljriDg the dXtssce by tha
the anile or grsdlenC. Table XIV.
BXCOSHAISSANCB.
Eipiaiiattan of use of Tables 11 and III :
Ralr. — ^From the llQe of the given Ki'adl^ot' take out the tabular
numbers correspwniilng to each of the flguces of the given dtetance,
iepinnlny at the right, and set them dowu ; each one place to the
left of the ODe above it. Retain the ciphers at the b^glanlng of the
Ust tabular Domber taken out. If an;. Other left-baad cipbere ma;
be dropped.
Add tfae tabular numbers, and point off from the left the number
ot places equal to tbat of tbe left-band figure ot the distance,
Botntting any left-hand ciphera. The result Is the difference of
«leTHtloD. In tbe same unit as tbe distance.
Bsamplfs. — For tbe dllTereucp of elGTBtion correspondlns to a
gradient of 3° and a dlatance of 6.273 feet on tbe slope—
From Table HI—
For 3 opp. 3° and under 3, 15T0
For 7 opp. 3° ana uuder 7, SB03
For 2bpp. 3° and under 2, 1047
For S opp. 3° and UDder 6, 031 40 retain leading cipher.
:b place, point off 4, 032B. 2^0
88 ENGINEEB FIELD HAHTJAi:.
2d. What difference of elevation for gradient of 5% and horizontal
distance of 7,180.56 yards?
From Table II —
Opp. 5** and under 6, 6250
Opp. 5° and under 5, 4375
Opp. 5* and under 8, 7000
Opp. 5" and under 1, 875
Opp. 5"* and under 7, 06125 retain leading cipher.
7 is in 4th place, point off 4, 0628. 299000
Diff. of elevation = 628. 299 yds.
18. Barometric leveliiis. — The weight of the atmosphere at sea
level is 14.703 pounds per square inch, equal to the weight of a
column of mercury 29.92 inches high, or a column of fresh water
84.7 feet high.
The aneroid barometer records the pressure of the atmosphere
in inches, the same as a mercurial barometer, .the reading being
taken from a pointer moving on a circular scale. The corresponding
elevation in feet is also shown on the dial of the aneroid barometer.
It must be carefully handled as it is sensitive to shocks. A screw
head will be seen through a hole in the back of the outer case by
which the needle may be brought to any desired reading, and the
instrument corrected whenever it can be compared with a standard.
With the aneroid, corrections for instrumental temperature can not
be made, and for this reason small pocket instruments are preferable,
as carried in the pocket they are not exposed to so great changes
in this respect.
The pressnre of the atmospliere irarle« with the altitude
above sea level, and it also varies with the moisture, temperature,
and latitude, which do not depend upon the altitude.
In measuring altitudes with the barometer these other causes of
Tariation must be eliminated so far as possible. It is best done by
simultaneous observatfon at both stations. If the stations are not
far apart all disurbing conditions will be substantially the same at
each and therefore eliminated, except temperature, which, with con-
siderable difference of altitude, will always be less at the upper than
at the lower station.
If 9imult(meou9 observations com, not be made, the stations should
be occupied with as little interval of time between as possible, and
better results will be obtained if the time of observation can be so
chosen as to take advantage of calm, bright, dry weather.
When the hygrometric conditions are very uniform an aneroid
read at intervals on a day's march over a rough country will give
a fairly good idea of the profile.
mBoomiAissAircx.
19. Table of elevations above sea tPvel from bi
(United States CMBt and Geodetic Survej), (or i
condltiona and mean temperature of 50° F. r
Bmo
n- Altitude
Diff
Barom-
Altitude
DM
Baro
n- Altitude
Dur.
above
Ibf'
eter
above
lor'
above
lor_
nadi
ig. 9ealec«l.
reading.
sea level.
IndLi
. Firt
F«(
Iw*e,,
^■.
Fat.
Znrt*
-
Frit.
13.787
-lS-1
22.2
M
-IS. 2
t2
2«
-10,3
13,817
10.3
13 468
5
«
2.1
10.3
13,318
8
17
10.1
13,172
ISCOS
n:«
27
10!i
12,879
S8
lao
ll',^
I™
li
2
S
8
LI
V.
9.
1
13." 7
».
13.7
i
13.1
13.1
13.3
2
6
^7
iii
I
fi.*
42
13.2
a 9
29
9.
10
2
S,
a
13.0
0.3
3 M3
31
18
12.8
3
1
O.M
o.s
0.7
5 458
t 308
B,
3 39
1^3
5
0.7
7 274
S
0.8
9.
e »
laa
I
lOB
0.5
30
0 OO
9
3S
12.5
g
0.5
9-
12.5
28
0
899
0-
0,1
9.0
890
27
12.3
3 j 3
0.3
^_
5 -451
8.9
H
EHGIVEXK FIELD XAKTTAL.
Tablh V.
20. Coelilclent« for temperatnre correction. — ^Argument
(* + *')=Sum of temperatures at the two stations:
<+<'.
Coefficient
C.
<+«'.
Coefficient
a
t-\-t\
Coefficient
a
•
0
-0.1024
o
60
-0.0380
9
120
+0.0262
10
—0.0915
70 .
-0.0273
130
+0.0368
ao
-a 0806
80
-0.0166
140
+0.0472
80
-^.0698
90
-0.0068
150
+0.0575
40
-0.0592
100
+0.0049
160
+0.0677
50
-0.0486
110
+0.0156
170
+0.07T9
m
-0.0380
120
+0.0262
180
+0.0879
#
fixamples:
Station.
Sacramento.
Summit
Temper-
ature.
F.
59.9
42.1
From table of elevations Sacramento
Summit
Diff.
t+f « 102*
.*. C - +0.0070
.*. Temperature correction, 6,913.7 x 0.007
—12.7
6,90l!o
6,913.7
+48.4
H
-= 6,962.1 feet.
Station.
Barome-
ter.
Temper-
i^ure.
l/Ower
■
■
Inchet.
28.076
22.476
"F.
57.3
T?M)er
38.5
From table of elevations Lower -= 7,867.0
Upper -= 1,807.0
Difif. = 6,060.0
t-\-t' - 96«.08
.'. C — +0.0004
.*. Temperature correction, 6,060 X 0.0004 =- +2. 4
H = 6,062. 4 feet.
21. U«e of compasses. — A good needle requires time to settle even,
when the case is firmly supported, and the user should cultivate the
knack of catching it at the middle of its swing, which is the deslre<l
reading. If the compass can be supported, it is always better to do
B'^ Then the sight can be carefully taken and the position of the
BBCONKAISSAKOEw Si
eye changed to read the needle. Wait till the Bwinggeta down to
4" or 5*, which it will usually do in a few seconds. Then catch the
highest and the lowest readings on the same swing and take their
mean for the true reading. If the first swings are very large, catch
the needle with the stop near the middle of the swing and release
it quickly. This will suddenly check the swings and shorten the time
in which the readings can be taken.
In using the box compass without a support hold it sufficiently below
the eye, so that the swing of the needle can be seen. Point the edge
of the lid in the required direction, catch the needle with the stop
in the middle of a swing and hold it stopped until the reading is
taken. Stop readings are less accurate than sight readings, as the
needle may be displaced slightly when off the pivot. When the stop
is used press it quickly and firmly. Always sight a fixed-card compass
from the south end of the card and read the north end of the needle.
With the prismatic compass the stop is not used except to check the
0vrings. Utilize a support if practicable. The prism having been
adjusted for focus, as already explained (par. 8), adjust the case so
as to bring the scale into focus, and when the swings become small
read the extremes and take the mean.
Compasses for night marching are on the market, but are not very
reliable. They have the dial rendered luminous by a paint. After
exposure to the sun or strong daylight they give off light, at first
rather strong, but rapidly diminishing in Intensity. After a few
hours they are not bright enough to be of much use.
The surest preparation for night marching Is a provision for
illuminating the compass by ordinary means without allowing the
light to be seen.
22. Tb determine the de^llnatlov of tbe compass s
First method; from fke »un. — Prick a Mtball hole in a piece of tin
or opaque paper and fix securely over the south edge of a table or
other surface perfectly level, so that the sunlight coming through
the hole will faW .on a convenient place on the surface (fig. 9). The
hole may be 2 feet above the table for long days and 18 Inches for
short ones. Half an hour before to half an hour after noon mark
the position of the spot of sunlight on the horizontal surface at
equal time intervals of about 10 mlnuteg. Draw a curve as bd
(fig. 9), through the points marked, and from point c in the hori-
zontal surface and in a vertlccLT line with the kole a sweep an arc
ej intersecting hd in two points. The line cff, drawn from c through
a point on the arc midway between the intersection, is the true
meridian. The line bd illustrates the method mecgiy. its form varies
with the sun's declination.
Second method; from the sun or a star. — -Observe the magnetic
bearing of the sun, a planet, or a bright star at rising and setting on
the same day, or at setting on one day and at rising on the next.
Take the difference between the sum of the rising and setting azimuths
and 360". One-half of this difference is the declination of the compass
or variation of the needle, east If the sum of the azimuths is less
than 360** ; west, if it is greater. In nslngr this method, the ob-
servations are better taken when the object is just above the true
horizon, or at a gradient of zero. This can usually be done if a high
point is chosen for the observations. If It ean not be done, be care-
ful to take both observations with the object at the same gradient.
This is most important ^rith the snn. Under the least favor-
able conditions an inequality of 1** in the gradients at the times of
observation on the sun may introduce an error of J* in the result. If
using a star, choose one which rises nearly east from the point of
observation, and the inequality of a degree In gradients will not be
material.
The change in declination of the sun between observations can not
affect the result more than J".
Both observations need not be made at the same point, but should
not be more than 10 miles apart in east and west or north and south
directions.
r
36
EHOZNEEB VIILD JCANTAL.
<'>,:
Of
0
E
"^^
°/.:5>..
Slg.ll
BMP
0
BECOlTKAISSAKeE.
87
The two foregoing methods are applicable in the northern or souths
em hemisphere.
Third method; prom Polaria. — The true north pole is about 1* 12'
distant from Polaris on a line joining that star with one in the
handle of the dipper, and another in Cassiopeia's Chair (fig. 10).
One of these stars can be seen whenever Polaris is visible. The
polar distance of Polaris is decreasing at the rate of 19'' a year.
It also varies during the year by as much as 1'. The latter variation
may be neglected, and the former also for a series of years.
Imagine Polaris to be the center of a clock dial, with the line
joining 12 and 6 o'clock vertical and with the position of one Of the
lines described considered as the hour hand of the clock. The dis*
tance in asimuth of Polaris from the true north may be taken from
the following table :
Tablb VL
23. Table slioiving; tlie asimutlis of Polaris in different posi-
tions with resfkect to the pole. Bpoch 1911 ; polar distance 70'.
Latitude 0° to 18' north. This table may be used until 1930.
Clock reading of—
Aei-
muth
of
Polar-
is.
Clock reading of—
Asimuth
of
Polaris.
Clock reading of—
A»i-
of
Polaris^
1
Cass.
z
Ursae
Mai.
8
Cass.
Z
Ursae
Maj.
8
Cass.
Z
Ursae
Maj.
Xn:30
VI:30
18
ini:30
X:30
e /
49
VIII
II
358 59
I
vn
85
V
XI
35
IX
III
358 50
1:30
VII«0
4»
V:30
XI:30
18
X
IIII
358 59
n
VIII
61
Vl:80
XII:30
359 42
X:30
iiiiao
359 11
in
IX
70
VII
I
359 25
XI
V
359 25
nn
X
61
VII:30
1:30
359 11
XI:30
V:30
359 42
For higher latitudes add to the small azimuths or subtract from the large ones, as
follows:
Lat. 19*-30% ^. Lat.5r-53%TV
Lat. 31 *-37% A. Lat. 56°-57% ^.
Lat. 38°-42% A. Lat. 58''-59°, A.
Lat. 43--46% A- Lat. 60"-61% A-
Lat.4r*-50%A.
It is well to keep track of the position of Polaris by noting it fre-
quently and taking the corresponding clock time. Then if on a
cloudy night a glimpse of Polaris is had, the observation may be
taken even though the other stars can not be seen.
24. For practical details of tlie observation, the following
may serve as a guide : Select a clear space of level ground not too
near buildings or any object which might cause local disturbance of
the needle. Drive a picket, leaving its top smooth and level, about
18 inches above the ground. Six feet north of the picket suspend
a plarab line from a point high enough so that Polaris, seen from
the top of the picket, will be near the top of the line (fig. 11).
Hie line should be hard and smooth, about A inch diameter. The
weight at the bottom of the line should hang in a vessel of water
or in a hole dug in the ground to lessen its vibration. Drive a
second picket in range with the first one and the plumb line a short
distance north of the latter. Make a peep sight by punching a hole
98 ENOnTEEBr FIELD MANTTAL.
about 1^ inch diameter in a piece of paper and hold it on the top
of the first picket ; adjust it so that the star is behind the plump
line when looking through the peep. Note the position of one of the
stars on the imaginary clock face at the moment the observation is
taken. Mark the position of the peep on the top of the first picket,
and lay a straightedge or stretch a line from that point touching the
filumb line to the second picket. Place the north-and-south edge of
he compass box against the line or straightedge and read the needle.
Find the azimuth of the star at the time of observation from
Table VI.
If the as. of Polaris (TaUe VI) and the readiii«r of tlie
needle are botli less or botli arreater than 180**, their dill, is
the deelinationi east if the needle reading is lean, 'west if it is
srreater. If one of these quantities is less and the other greater
than 180*» add 360** to the lesser and take the diff. which is the
declination ; east if after the addition is made the needle reading is
less, 'west if it is srreater than the tabulated az.
This method win jdve results true to within J*.
25. Distances passed over are ordinarily measured by the stride
of a man or a horse, or by the revolutions of a wheel. Distances not
passed over are determined by intersection or are estimated.
Paeincr on foot. — ^The length of a man's pace at a natural walk
is about 30 inches, varying somewhat above and below. A stride
equals two paces. Each sketcher must determine his own length of
pace by walking several times over a known distance. An unnatural
stride shouM never be taken. Knowing the length of a pace or step,
the measurement of a distance is only a matter of connting steps.
The counting may be done maitally, and with practice becomes a
sut>conscious operation, leaving the attention free to take note of sur-
rounding objects and conditions. The greatest danger is of drop-
ping 100 paces. It is better to keep a tally of the hundreds. By use
of a iiaee tally all danger of error is avoided.
On level ground careful pacing will give distances correct to S
per cent or less. The normal length of pace decreases on slopes.
The decrease varies with the slope and with the direction, wheuier
ascending or descending. The following table gives the length of
pace on slopes of 5*^ to 30*, corresponding to a normal pace on a
level of 30.4 inches.
Tablb VII.
Slopes. \ 0" 5* 10*
1
lo"
20"
19.7
26.4
25"
30»
Ltngthofstepa^^cemiin? 30.4 27.6 124.4
LngthofstepdecsceiKiin;: 30.4 . 29.2 28.3
I 1
22.1
27.6
17.8
23.6
15.0
19.7
For the same person, the length of step nsoallv decreases with
fatigue, Sketohers should test their pace when fresh and when tired,
and if there is an apprecl.iWe difference, nse one length lor the morn-
ing and the other length for the afternt>on work.
1*6- A distance on a slope measured by foot pacing may be reduced
to the correi't horltontal distance for plotting on the map by the
following table, which take* account of the decrease in length of
pace, T^ble Vll. and als^o of the reduction to the horizontal. Table
XI L This table can be used only when the length of pace has been
determined on level ground, which should usually be done. When a
considerable stretch of road Is fo\ind with fairlr antform slopes, a
aptvial a\-erage rating may be made over a distance involVmg a
fairly representative range of slopes and this amrsfr ratinff mity he
used witnont reduction.
ABCOmrAXSSAirDB.
s >
d
0
h
0
n
0
0
3
i
o
I
o
•a
Ik
a
o
M
ki
O
A
0
o
s
s.
o
I
1.
s
^
s
o
o
Q
e
o
A
P
i
p«
^
o
P4
o
ft
a-
ui oS eiri cd c3 »$ bl ^ ^ 0^ fh |sl CO oi ^ ^ c^ Cl
300>^f-4'He<4C4CS9Q
E8
e4 0oot^kOco«-io>aecD'^toaeoe^'^cox
*HOO»aet«r««ow3<<«coeseo-4*udtob>ooa>
aoo»oo*HC4cQ'^'^>0(p-4*04oaocO'<f*c<4
^ 2fi »^ i^ «^ -5 2^ »^ "5 d '^ «^ sa ^ 3? "J «i5 1:
« ® ® o *H « 6» w >* « « s; 43 g c» «o ■«•• es
oot>.«0"^oooj»iooob-W"*e40PO<0'^ci
ICO^W3«<
00 M e» *-i o o Ok flo r- b- «o c> c« wa 00 ?H ««it b-
9 SP £2 Srf Gr ■!! O t^ y »*< 90 1^ t«-«p »o »o ^ M
5J jH ^ oJ gd t^ «d wi -^ CO CO ■<i' trf t^ cp cSfrJsi
t»«OTt<C0C^.MO>00t^U5Tt<»HO0»ONO>»C0
9^ S !i ^ o o^"^ f5 •-* o> 1^ «d ^ ^ e«i rf a; od
«DOt>-eOOO'^0»Oi-HOCIOOTj<0«DC«00'*
I N cS ^ '
g p »-< c< c6 ># >o. to br 00 OS 35 OQ b- i
■^■*-*<»Ctf5«><Ot>-t^<»OOW«0 0'*<000«50
■ ••III
• •••••
• •••••■•«•
■ ••••••••I
80 EHOIKEXE FIELD XAHITAL.
Table VIII elves directly the horizontal equivalents of the distances
usually occurrlne in foot pacing. If desired, other distances may be
obtained by combinations.
From 1 to 9, take the first figure, left-hand cipher included, of 100
to 900 for the whole number and the second figure for the tenths.
From 10 to 90, take the first two figures, left-hand ciphers included,
of 100 to 900 for the whole number and the third figure for tenths.
For 290 take 100 + 190 ; for 440 take 140 + 300, etc.
Example : For the horizontal equivalent of 738 paces on a 5** rising
slope.
700 + 30 + 8=«632.8 + 27.1 + 7.2=667.1.
28. Pacing mounted. — The average valk of a horse is a mile in
16 minutes, or S| miles per hour, making 120 steps, covering 110 yards
per minute, the step being 0.916 of a yard, or 33 inches.
The average trot Is a mile in 8 minutes, or 7i miles an hour, mak-
ing 180 steps, covering 220 yards per minute, the length of step being
1.22 yards, or 44 inches.
It will srenerally be found more convenient in pacing, both
on foot and mounted, to count the steps of one foot only, and multiply
the number counted by the stride of one foot, which is twice the
length of step given above. In this case the number counted is
doubled for use with the tables and scales given herein.
Timinar. — Counting the steps of a horse diverts the attention more
than is desirable, and it is better to determine distances in mounted
reconnaissance from the times occupied bv the horse in passing over
them. A stop watch is the most satisfactory timer for this pur>
pose. The ratlnip is done by ascertaining the time required to pass
over a known distance. Time and step ratings should be taken
together by counting and timing at once. Ratings should be taken
before the reconnaissance, if possible, but for short stretches of hasty
work the averages given above may be used without serious error.
Horses travel better in pairs, and two men should be sent 6ut to-
gether, one to do the sketciiing and the other to give his entire atten-
tion to taking the time and keeping his horse at a regular gait. It is
better to rate the pairs together. If it has not been done, take the
rate of the timer's horse.
When a sketcher is traveling with a party and must keep their gait»
an occasional count of his horse's steps for a minute or two will give
a special scale for use in plotting.
29. The speed of a horse over road grades, even in moderately
billy countries, is not affected by the slope sufficiently to make an
allowance necessary. Distances up and down grades measured by
timing in mounted reconnaissance will require no correction except
that to the horizontal. Table XII, which may be applied if the slopes
exceed 5" or 6**. This statement does not apply to distances
measured by mounted pacing or counting the steps of a horse.
30. The fvalk is tlie normal arait for reconnaissance. — If
greater speed is necessary, the timer may go on while the sketcher is
taking angles and plotting, the latter taking the trot or the gallop and
overtaking the. timer just l>efore he reaches the next statKm. This
method should be used only when the required distance can not be
covered at a walk.
If circumstances require short distances to be covered at a trot or
gallop, the times may oe reduced to walking time by multiplying by 2
for the trot and 3 for the gallop.
31. The odometer is an instrument for recording the number of
revolutions of a wheel. The adopted form is in a leather case, 4i
inches in diameter by 2i inches thick (figs. 7 and 8). It is attached
by straps to the front wheel of a wagon (fig. 7). To read, the case is
opened, the registering train withdrawn, and the number of revolu-
tions read from the scale. Multiply the diameter of the wheel by
3.1416 for the circumference ; multiply the circumference by the num-
ber of revolutions for the distance traveled by the wagon.
The bearings of the odometer must be kept free from grit and may
be oiled with fine oil used sparingly ; gummy oils or grease most nik
XSCaSHAZBUmiE. *t
tM Died. If good oU la Dot to be' hid. nib the benringi with • soft l«ad
Odometer readings sre Tsluable as a rongh check od a day's march.
The; are not accurHte, but are tree from large errorB. Two Invtru-
- "- - -■- e wagon will not alwajB agree. "- "■ — •*-
mud or Band, thert IB I
■lip, aometlmea posltlTe a
Tablb IX.
to wheelB Si
Diameter
36 U
48 i)
Biae of ivhceta of
ponton (light) tool
"• 7), ft laehBi:
e military fragons; Ambniance, 30} Inches:
, ^..--., , -21 inches; escort, 441 iDchea; ponton
(heavy), ili iuehea; Army sli, 4T) Inches.
S8. BIatliB>tt<»> of dlBtanepa Is a knack wblcb may be culti-
vated by practice to a d^ree of arcuracy far beyond that whl<!h Is at
Brat attainable, and quite sntHclent for the locstlon at many oUectt
off the traverse line. Short diatanceB are more closely estimated than
longer onee ; those on a level, thao those np or down hill. When the
tntermediats ground can be seen, the estimation will be closer tban
wben It caa not
A tvugJt eallmotc at distance may be made from the velocity o(
sonnd, as by knowing the tine that elapses between se^ng and hesil-
Ing the dtseharee of^a gim. or the fall of an ax. Note the time In
seconds nnd multiply by 4(M) for the distance In yards.
DlBtances across water are usually nnderestlmated. ..
of the visible horizon on water Id nt«c« 1r 1.225 -/W; H being the
helebt of thP observer above the water surface In feH.
A cartridge ur other emnll bcavy object lastened to a string 10
Inches loni; and allowed to swing througlit a small angle or arc will
t halt HI
34. ■
olnt by intepaectton Is c
10 known points. As each (
lasB through the unknown p
ne by
these
takliiB azimuths to it f
silmuths when plotted
mnst be at their Internee
two visible linowu points by (akinc an azimutb to each. From the
known points plot the correapondluK back mlmulhi and they will
Intersect at tbe point of observation. This proceas la called pe-
■eetloB. rt Is subject to errors of local attraction. (Far. 0.)
The accuracy of a location by Intersection la alfocted by the rela-
tion of the azimuths and of the distances. The greatest accuracy
resnlta when the .iilmutba differ by 00° or 2T0° and the distances are
eqnal : In which case tbe two azimuths and the bese form n right-
angled triangle. A difference of azimuths of less than 30° or more
than 3.<tO° should be avoided.
Brpora In lenictb of tfee base, or dlatanee between the known
points, affect the distances In the same proportion. It tbe base Is G
or 10 per cent In error, botb the distances will be In error in the
same direction by the same percentage.
U ENOIHSBB, TIELD JEAKUAL.
Distances are most easily determined fTom iDtersections by platang
the palDtB and ecallng. The dlBtances are horizontal. It gradlantB
are taken at the same paints ae the axlmutha or at one of them, tbe
elevation of the unknown point ma; be determined after the dlatauce
h^H been scaled.
35. Tape ekslaa are adapted for the accurate measurement o[
considerable distances. The tape chain Is a Rteel tape detachable
from the reel on which it la carried, and with a handle at each eud.
It is graduated in lest, the last foot to tenths and the last tenth tir
hnndredthB.
Metnlllc (opes are ot linen with wires woven In longitudinally.
Tbey are graduated In the same way as tape chainE. and al^o In feet,
inches, ana elEbthe. Metallic tapes are used for the exact meaaore-
ment of short distances, as dimensions ot buildings, lengths of
bridges, etc. They stretch slightly, bnt not enough to introduce
appreciable prror.
In niilnK <npps note cBretnllr whether the small divisions are
Inches or tenths of feet. See that the Ant Krndnallon Is the
proper dlitanee from the end. and It the tape bas been spliced
note whether the graduations on either side of the epUce are the
Rnlrs nre usi'S for measuring short distances and dimensions and
are usually graduated In feet, inches, and sliteentbs (Sg. 45).
Eules appro ilmately correct may be Improvised Id several ways.
If a rule or rod graduated to feet be grasped in both hands, palms
down, with the outside edges of Ibe hands at consecutive tout marka
and the thumbs extended toward each other along the mle. the tips
of the thomba will meet or pass, iind by carelnlly ootlng their rela-
tive positions a foot may be approximately reproduced at any time
by graaping a stick In the hands, placing the thombE In the proper
position, and marking the outside ot tbe bande. A length may be
nieaanrpd in feet by paBsing along it hand over hand, ^acioft first
the edges of the hands together and then the thumbs as described.
his ewct'^. „
I Inch in dlameier.
Jt (■ Imprnctlnahlc to adapt ana AdheFC t<
with the system be Is tamlllar with and should he
The following table wUl convert nnlta of one syi
the other:
Table X.
Sa. Table for oonTeralon i
Tablb XI.
37. 16tlui of an iaeh in deelmalu of an Infill t
063
A
125
1S8
250
31S
1
375
« H
750 I 813
38. R«an«ti<»n to tbe lioi*la<vntal. — Dlstftnbes m^asufed along
a slope may require a csorrectioii "beforo plotting thHn on a map, as aH
map distanced are, or are supposed to be, toeasured in a horizontal
plane. Snch corrections, when made, ar^ called r«dnction to the
Iftoriaontal. The following table gives Horizontal distances corre-
sponding to sloping' dlstahces for gradients up to Sp**. This table is
to bo need In the same war as Tables II and III. The correction for
slopes of 6** and less is too small to be 'plotted dn the customary
scales and ia dSuttHy negfected. Itt flatop wtlifcary rolling country
the correction win rarely be neeessary. r -
, \ TABtE XII. ' * '. .
39. Hor|3EOnfal d|«tanceii for jrradlcnt^ of 0** ,to 30* corr.espO^(it-
ing to distances on the ^ope ^ ,.. . " ,
ii
-H 1*-
-1-.; — ■ — i4-
• tt
Hi H III' I 'll H I I
9$
1
2
3
4
5
6
7
8
9
10
12
14
16
18
20
22
24
25
28
27
28
29
30
.' ^oriaon^ai distances for sloping (iis^nces of—
. 'i .1.1.
00998
09994
09986
09876
09062
09945
09925
09903
09877
00648
09781
09703
09613
09510
00397
09272
09135
09063
08968
0S910
08829
08746
08660
1
' > M.
• ' H
2.
^
3
1
*
1
•5 ,
■ ■ 6. ,
.. 7
.8. .
19097
a989&.
39094
r49902
. 59991
< •
09980-
79988
19988
29982
39976
49969
59963
09967
79961
19972
29969'
69945
49i31-
> -atd^lA
'69001
79890-
19951
99927
39902
I 49878
50854
69829
79805
19824
2i88a
39848
49810
d0772
69783
79696
19800
29886.
. 30781
49726
59671
«06i«
.7956»
19861
297?6
39702
' 49687
59553
199478
79404
19805
29708
30611
40513
d9416
69319
79221
19754
29631
39607
49384
59261
69138
79015
19696
29544
39392
49240
590S8
68936
78785
19563
29344
39126
4^907
58689
68470
78252
19406
29108
3881^2
48515
68218
. 67921
77624
19225
28838'
38450
48063
57676
67288
76901
19021
28532
. 38042
47553
57063
66i>74
76084
18794
28191
37^S
46085
56381
65778
75175
18544
^7815
37087
463i>9
55631
64903
74176
18271
27406
36542
36252
45677
54813
•63948
73084
18126
27189
45315
64378
63441
72505
17976
26964
35952
44940
^
62915
71903
17820
2^88
35640
44550
62370.
71280
17659
17492
35318
44147
5^7
61806
70636
26238
34985
43731
61223
69969
17320
25081
34641
43301
5^961
60622
. 69282
,. .9
^89980
80945
89877
89781
89657
88507
89329
89124
68892
88633
88033
87326
86513
86505
84572
83446
82219
81568
80891
80190
79465
78716
77942
The horizontal distance corresponding to anp sloping distance, and
any angle or gradient may be found by multiplying the sloping dis-
tance by the cosine of the angle, Table XIY.
94346"*— 17 3
84 . EHOINEEB. FIEI<D XAHUAL.
40. The protractor is an angular scale of equal parts used for
plotting azimuths. That adopted for reconnaissance is the rectangu-
lar form (figs. 12 and 13). It is graduated on one face, which will
be called the A face (fig. 12) from 0' to 180°, and on the other, or
B face (fig. 13) from ISO" to 360*. The graduation is clockwise on
both faces. It has a scale of inches and tenths along one edge. The
protractor may be used as ruler, scale, triangle, and parallel ruler.
To plot a sriven asimntli from a arlven point, draw a
meridian through the point. If the azimuth is less than 180**, lay
the protractor down A face up with the center at the point and the
edge on the meridian, 0** to the north. Make a pencil dot on the
paper at the proper graduation on the edge of the protractor. Move
the protractor so that one of its edges passes through the two points
and draw a line, which will be the desired azimuth.
If the azimuth is more than 180*, lay the protractor down B face
up, 360* to the north, and proceed as before. The moving of the
protractor after setting off the angle and before drawing the line
may be avoided by adding a coanter-cloclc^vi»e graduation to
the protractor. The sum of the two graduations at any point will
be 180*. Place the center of the protractor and the given azimuth,
read on the eounter-cloeU'wise graduation, on a meridian, and
slide the protractor up or down, keeping the two points on the
meridian until one of the long edges passes through the given point,
when the azimuth may be drawn along that edge.
A semicircular protractor is shown in figure 14. It is usually
double graduated, in opposite directions from 0* to 180*. With this
form an azimuth may be laid off and the line drawn along the diam-
eter without moving the protractor. Lay the protractor down with
the center on a meridian. If the azimuth is less than 180*, place
its number of degrees on the coiinter-cl<»cUivi»e scale on the
meridian north of the center (fig. 15). If it is greater than 180*,
subtract its number of degrees from 360 and place the difference on
the clock^vise scale over the north end of the meridian (fig. 16).
In either case slide the protractor up or down, keeping the center
and the graduation on the meridian until the diameter passes
through the point, when the azimuth may be drawn along the
diameter of the protractor. Figure 17 shows a triangle graduated
for use as a protractor.
41. ImproiFised protractors. — If a rule is at hand, a protrac-
tor may be made as described for slope board in paragraph 14 by
extending the 1* graduations around a half or whole circle. If
-vvitlioat compasses, measure off the radius on a piece of paper,
stick a pin through one extremity for a center and a fine pencil point
through the other extremity and sweep the circle.
If ^vithoat a rale, fold a piece of paper carefully through the
fniddle. The folded edge should be straight. Flace the ends of the folded
edge together and fold again. The two edges now make an angle of
90^. Fold again through the middle and the angle will be 45*.
Now fold in three parts and the angle is 15*. Spread the paper out
flat and the creases will represent radii of 15* inte/vals. Tnese may
be divided into three equal parts by the eye, and the protractor will
then read to 5*.
The hour graduations of a watch ure 80* apart, and the minutes 6*.
42. The scale of a map is the ratio between dimensions on the
map and the corresponding dimensions on the ground. If the lengths
on map and ground were expressed in the same unit, the scale ratio
would always be expressed by the number of ground units corre-
sponding to the map unit. If 1 inch (map) corresponds to 120,000
inches (ground), the ratio, or scale, is plainly l-i-120,000, or as
usually described, 1 to 120,000. This fraction is called the repre-
sentative fraction, and designated K. F. But ground distances
are so much greater than map distances that they are ordinarily ex-
pressed in a larger unit, which makes the «cale ratio less apparent.
If 1 inch (map) equals 10,000 feet (ground), the scale is still 1 to
]
xsoonrAXSiAVOX.
t9
1^
^^^5§SS^§i^mmvM^\ffil;i;lll!IJi^^^^
Id 59 n 70 m w lio lio an m lio
0 100 TO THE FOOT,
^ B) M ao 4A
Ilililiililiii'liiiilNiiliiiiliiiilrTrrl
8^^
0
00
miiiliiiiT
10 TO THE INCH.
SIP
U.S.
MiiliiimniliiiiliiiiliHiliiiiliiiiliiiilun
i
mS^S
Flfir* 12. A Face
SSJSSSSSSsSSS^:^^^
sS-
I'
1^
m a0ttO2SOMOStOMOSMSWSiO m
ililll'lilinillllllllnlllllllllTlllllllMitlTJ "1
Flff. 16« BFaoe
0
00
ilittiliiiiTnnliiiiTiiirliiiitT
Fig. 14
S S
Fig. i«. Tig. le.
Ftg. IT.
U ENOnrSXA ]mE£D ICANTTAL.
120,000, because 10,000 feot equal 120,000 Inches. Tlie map unit
is almost alifvays inches, iience a good rule for obtaining the
scale ratio is to reduce the given number of ground units to inches,
which will indicate the ratio.
Another method of stating scales, much employed in military map
making, is to take ratios which will give i, 1, 2, 3, 6, 12» or 15 inches
on the map to 1 mile on the ground, and call the scales I, 1, 2, 3, 6.
12, or 15 inches to the mile, Sueh scales can be put into terms
which express the ratio by dividing 63.360, the number of inches in
1 mile, by the number of inches given in the scale. Thus, 1 inch to
1 mile equals 1 -i- 63,360 ; 2 inches to 1 mile equals 1 -i- 31,680 ; 3
inches to 1 mile equals 1 -^ 21420, etc»
The scale ratio is true for all upits. If a scale ratio is
1-7-9,600. 1 inch (map)=9,60a inches (ground) ; 1 foot (map) =
9,600 feet (ground) ; 1 meter (map) =9,600 meters (ground), etc.
When the scale of a map is changed, as by reduction or enlarge-
ment, the R. F. changes too, and hence tne ratio should not be given
on maps which are to be reproduced. A linear scale should be
dra^wn on every map. This will be enlarged or reduced with
the map and will always be true. Such a scale is ^Iso very conven-
ient for taking distances from the map. It consists of a straight-
line divided into equal parts which are numbered with reference to
the relation between distances on the ground and distances on the
map. The numbers relate to distances on the ground and the grad-
uations, or lengths ^et off on the line, relate to distances on the map.
A distance on the map equal to that from the zero of the scale to any
graduation corresponds to the tlistairce on the ground represented
by the number of that graduatlbn. Scales are designated by" the" unit
of their parts, as scales of : inilos^ .mea.les of feety scales of
meters, etc.
A scale might be constructed bv drawing a scale of inches on the
map and placing opposite the divisions the numbers expressing the
equivalent ground distances. It Is customary, however, because more
convenient, to take the numbers at intervals of 10, 100, or 1,000, or
multiples of them, and mak^ the divisions of the line correspond. A
scale should be divided into a convenient number of equal parts
called primary divisions. The zerO should be between the first
and second primary divisions, counting from the left. The primary
divisions are numbered from the zero to the right. The primary
division on the left of the zero is subdivided into smaller parts.
called secondary divisions, and these are numbered from the
zero to the left. The secondary are usually J or j^ of the prlnaary
divisions. " "
To take off any distance from such a scale, put one leg of the
dividers on the primary division next below the distance sought, and
the other leg on the secondary division corresponding to the remain-
ing figures.
Figures 18 and 19 give scales for the usual range of topographic
maps, which may be taken off on the edge of a strip of paper and
transferred to a map. Figure 20 gives scales for plotting distances
measured by pacing on foot, and figure 21 for those by pacing
mounted. '
Scales may be constructed on strips -of paper, wood, celluloid, or
metal instead of on the map, and are then called plottingr •ettlen.
The scales given in figures 18-21 are plottiftg scales. A distance
may be taken between dividers from any map and read by applying
the dividers to the proper one of these scales.
These scales are not engraved and can not be relied upon w^lthin
1 per cent. They are sufficiently exact for reconnaissance and, ia
fact, for most topographical drawing and scaling.
43. A series of points connected by azimuths and distances ist
called a traverse, and the operation of determining the asimuths
and distances is called traversinar* The latter ^rm' is usually
EECOHHAISSAXOB. S7
Sig. 18
R. F.=-'-^=-8!33 to f**633''6 to 1 mile.
10 987654821 0 ._ 10 feet*
R. F. = ^ — 10' to f -— 528" to 1 mile.
10 9876548210 10 feet.
R. P.— 55o*"4l'.66 to f— 126!? to 1 mile.
50 26 0 50 feet.
I I
R. F.= 7?;?r = 50' to f=» 105^6 to 1 mile.
600
50 26 0 60 f eet^
-I
*
R.F.= 4^=352' to r— 15" to 1 mile.
100 50 0 IJOO 200 yds.
R. P.— 5^=440' to f— 12" to 1 mile.
MO go 0 100 300 yds.
H H H H H I I ' I
R. F.=^ 10^=833. 3 to l"=6rS4 to 1 mile.
100 0 100 200 800 400 500yd».
R- f-~ 10560=' 880' to r= 6" to 1 mile.
100 0 100 200 800 400 600ydfl.
HHHHHI
\ \ \ V i
98
EHGINEEBr FIELD MAHIFAL.
R. Ff
1
20000
Fig. 19
1666^7 to 1«3'.'l7to 1 mile.
100 0
HIHHIII i:
fiOO
lOOayds.
I — I "I
R. F— 2n20 ~ ^^^^ ^^ ^ "" ^"^^ *° ^ "^"®'
100 0
soo
1000 yds.
R. FT=co5nn -= 4400'io f = f.2 to 1 mile.
52800
1000 0
H l-j l-l l-l l-l I.
1000
2000 yds.
R- FT=g3^=-5280' to r— 1:'00 to 1 mile.
1000 0
M M M MT=n=
1000
2000 yds.
3
I R. Ff=^ 26720 ^^Q^^Q' ^^ 1—0:50 to 1 mile.
1000 0 1000 aooo aooo 4000 soeoyds.
HyHHHI 1 ^ I 1 I
R. F.=g3^^oQ=52800' to f=10 miles to Xl
10 9876543210
10 miles.
IE
3
f R. F-T5oZrv.n -132000' to f==25 miles to iT
1584000
10 0 10 20 30
40 miles.
MMMHMt-
I
3
BSCOmrAISSAHM.
40
ENCfimSSB ITBXD HANTTAL.
<D
o
"to
mSCOKXAIggAKaX. u
:o Indade all aztmutbi, dlaUDces, aaa eleTatlons taken
Ina such a Hup
He line wltb eleratlang along It may aleo be called a proflle,
r tllF^ «ipreHg purpose of taking the
and wl . .
etenstiona, the opentlOQ ..
ground and the plot of It on pupt
DiBtancee In topography 8» ~
botb can not coDVfnlfntly be
usual to take a scale Cor cicrn
larger than the scale o( dlstaii
o( the two- scales !h called
~ ' jBtity feet to the Inc '
t elevations that
otberwiae by
plot tt from tbat point. In auch c
units to the right o
4S^Trav«
e the
L lint' a
right angles t
e denoted
nee of 300
; through
■mliiK nltb I
uiuu iun-.~iourths of an incL _.
S;e of the noteboot. Select for the starting point some ooject Or
. nt which can be Identified by dcficrlptton. Standing at this point
light with the compass toward some object — tree, stump, telegraph pole,
or stone^that will serve as the second station of the tFaverse line.
Note the reading of the compass and record It In the center coluDin
48 ENOIHESK 7ISLD XASTTAL.
of the notebook at the bottom of the first left-hand page, making also
the symbol for O 1. Observe and record also the asimuths of any
other objects which are to be located from 0 1. All the obserTatlons
taken at this station are written in order in the central column from
the bottom upward and are bracketed together with the station
symbol. The name of each object is writt^i on the same horizontal
line with its azimuth— on the right side of the page if on the right
of the traverse and on the left side of the page if on the left of the
traverse. If elevations are to be obtained, observe the gradients
from O 1 to the several objects and place each in the notebook next
to the corresponding azimuth.
Proceed toward 0 2, counting paces. Halt when necessary to sketch
and measure offsets to objects on either side of the course, to take
bearings of intersecting roads, paths, streams, etc. When a halt is
made a mark is scored on the ground, the distance in paces from the
last 0 recorded in the central column, and the desired notes made.
Distances along the main line, asimuths, and gradient angles only
are refiorded in the central column. All descriptive matter relative to
side objects is placed outside of that column on the side corresponding
to that where the objects lie. Return to the scored mark and resume
the pacing, beginning with the number recorded at the halt, so that
the total count of paces at any point shall be the number taken since
leaving the last 0.
The center column of the page is taken to represent the line actually
paced and to be without width, so that offsets in the side sketches are
shown measured from the sides of the column and not from Its center.
On reaching the second 0, record its distance from 0 1, draw a
horizontal line across the page, write Q 2 in the center column above
the line, and continue as before to 0 3.
It is well at 0 2 to take a back azunuth on 0 1. This should differ
from the azimuth of 0 2 from 0 1 by exactly 180**. A marked discrep-
ancy indicates error in observation or the effect of local attraction on
the needle, and should be investigated before proceeding. If a back
azimuth is taken it should be the first observation made and recorded.
When opportunity offers, take bearings on distant bends of the road,
spires, towers, hilltops, tall trees, etc., and enter the angles in the
center column with the name of each object written beside Its bearing.
Endeavor to get bearings of the same distant object from several sta-
tions or from two stations at some distance apart. These, when
plotted, should intersect at a common point if the observed bearings
are correct and the compass has not suffered local disturbance. It is
not to be expected in work of this grade that an exact intersection of
more than two bearings can be obtained except by accident.
When a sketcher at any point of the traverse finds himself in pro-
longation of a line that defines or bounds a feature of the country,
such as a fence, the edge of a wood, a reach of shore line of river or
lake, a gully, canyon, or ridge, a face of a building, or a stretch of
road or railroad, its bearing should be taken. The same rule should be
observed when important features come into range with each other
from a point on the traverse. A valuable check on the relatlT^ positions
of such features is thus obtained.
If a traverse line is interrupted by any obstacle that Interferes with
the measurement of distance, its width should be estimated and the
pacing resumed on the other side ; or, for greater exactness, make an
offset, perpendicular to the traverse line if possible, long enough to
clear the obstacle, continue the traverse parallel to the original course,
and return to the latter after passing the obstacle by a second offset
parallel and equal to the first and in the opposite direction ; or, locate
points on the farther side by Intersections.
47. The unit of measure should be clearly stated lil tlie
notes. Ordinarily distances along the course are in paces, while
estimated offsets may be in paces, feet, yards, or fractions of a mile,
according to their distances, and also according to the unit in which
the sketcher finds he can make the closest estimate.
EUOnUBBAHai.
eoBlona of bulldlngi,
I to scale. Thef are
Imiwituit, muat b«
Bcovered b; means of
e biu been adjuated,
it bave to be cbaoKed.
ersioe witb compaas
>ta of papei ruled as
of nedlum bardnesl,
:e of twine 100 feet
tbe compasB, pocket
II, The tape measuce
deslsned to fscllltate
to tie central column,
I the offset distances,
I tbe centra] column.
d L, and eliminating
.'.«
ly tban they ci
■ are scales of tentbs
Kgea are plain ruled
iw the knSDgement
SO. TraiTerslDK wltk conpaaa aad dmivtiiK board. — Tbe
obserratlona are taken as la traversing with a notebook and compass,
but tbe tiBTerse line and such offsets as come iirltbln tbe limits of the
sketch are plotted at onre ; that Is, the map ts drawn as the obserrer
proceeds over the ground. A great advantage of this method Is that
iny large error la measurement la likely to be detected by the eye, as
... .. J _..,. »t J ._j j„ ^ corrected on
, . e prepared before-
It this scale can be pasted or
opposite the angular gradnatlon.
1^ sides of the sheet of paper should be letered N, E. 8. and W to
correspond with the polnis of the compass. It tbe paper Is ruled or
water-lined, the lines are taken parallel to the magnetic meridian.
Harlne observed the azimuth at Q 1, draw tbrougb the polDt deslg-
BiUng that station a line having the observed ailmnth. Ailmutli
lUies are erased finally as a role, and hence ibonld be lightly drawn
■nd with a fairly hsnl pencil. Prolong this line tn the direction of
0 2 far enoueb to surely reach that Q. If other azimuths are taken
It O 1. plot them alao, and oole on each the object to which It bears.
It the distance to (he object Is esllmsted. It mev be laid off on the
iilmnth and tbe position of (he object plotted a( once.
t O 2, lay off (he entire distance from © 1, and plot and
mark G ^. Erase tbe azimuth line beyond O 2 : take and plot any
other desired aitmutbs. If any of them are to points previously
sighted to, make tbe IntersecdonB and plot and marli the p'-'-
plottinB azimuths tf -'■•" ->■'--•- '• ■- ■—"— •- — i
part of tbe line ne^. ,„.
sketch and especially near tbe atatioii.
44
ENGorfiBE ]ri£i:.D manual.
/tern ar/cs£g/i.
>«— W«*-aartarmd>
e/k.
Courses A (9fsiis
Dt'sicmces
jRiSf^t'
J^€marjts^(^At^
Grossed wagon road-
running j£.ic fV.
OrossC'Ol oify Cr.
/ZdO— ^3<U J^6a<f running ACtS.
-^ jri. tAj-o uyh ^<yO i ne —
.Cr'^^/2.
./OO-
.Z30_
re
arm
M.
.Cu/t.
/BVQi
1256-
RRBh.
-Cr.
/oa.
/%, /r.^/Tr^
A 000.
3080:X
2766-
ZH65^
iPOAJldOO^
J-(iross*<i dry Or.
C7roj sed loayon roacL.
^r OSS ad dry Cr,
B./iBn.
Z3X)^
TT
1
J70O.
JSOOiX^OO^
'MSO^
.■r*ar mybT,. ,,
j0rr)ss,9oi fP^fg/^rooct
' »
t, •, »: 1 'r •;■.
-^o /^gi Prairie,^
' » 4 I
■HI 5
Jra^t
u.rfi .. .
JIA
1 1 « III i« I I > I ■ ,
.800.
eoo.
..230.
-Corn (& ^/isat.
/SO-J^
Cross ea^urayo/^ /yaoL-
.Corn A PP^eaf-
Craa^j c//y r'Ufz,.
C'^SO^
/230-
/SOX.S80.^
3'F-
jrs^Fo
Cross gdCf^ /Swicle^
arm //, — .
m3vc^-
^2.
^e/9aaayon road-
CulL.
^qa.
SO^J^a
^arm//,.
Cult.
J^rm/ZL.
.J2S.
£331
.200^
lM/Mji»f,a 6*3(f7iif-
VfOO.
OVOl.
Crm XT* i Coi*rti>y
/a^.fiarm//:.
£b//oU/irtgr tvap^n road.
iff]
-Sept. ^th,f900.
6''30'
A//«fisf*neest'ri y&'s.
£e^ inning
46 ENGINEEE FIELD UAJSTUAL.
51. The follovvlngr ontflt is desirable for traversing by this
method : A thin, smooth board 12 by 15 inches, to which the paper is
attached by thumbtacks or rubber bands, prismatic or pocket com-
pass, clinometer or slope board, a rectangular protractor, a plotting
scale, lead pencil. No. 3 or 4, rubber eraser, 25-foot tape, 100 feet
of twine, watch, pocket knife, canvas cover for board and paper, note-
book. A field glass is also very useful. Good work can be done with
a less elaborate outfit, or with improvised arrangements for some of
those mentioned. The drawing board may be utilized as a slope board.
52. A road sketch will be long and narrow, and two or more
stretches should be got on a board if possible. In this way a board
of the size indicated will hold a fair day's work. When a section
runs off the paper mark it with a letter, as A, and make a note. Con-
tinued at B. Mark the beginning of the next section B and write
Continued from A.
Wherever else a road runs off the map, make a marginal note
** To , miles/' giving the name and distance of nearest
settlement or conspicuous topographical feature. If the road crosses
one parallel to the main route, write also ** To crossing,
miles."
53. Traverslnir 'with oriented dra^vtnflr board. — A drawing
is said to be oriented when so placed that its true meridian is paralm
to the true meridian on the ground. When using magnetic aamuths,
making the magnetic meridians — ^map and ground — parallel, may be
accepted as a proper orientation. When a map Is oriented, with any
given point vertically over the corresponding point on the ground, a
ruler held on the point or station on the map, and pointed in the
direction of any obj^t gives the azimuth of that object on the map.
No angular measurements need be made. A compass is not neces-
sary, but it is very convenient as it affords the quickest means of
orienting the map.
54. To run a traverse l%y this method assume on the map
the initial point and the magnetic meridian, selecting them so that
the general direction of the traverse will coincide with the longest
dimension of the paper. Place the board over the first station ; lay
the compass on it with the north-and-south line parallel to the
assumed meridian, and turn the board until the needle reads north.
The board is then oriented, and must be in this position whenever
a sight is taken. It should also be level, as nearly as can be deter-
mined by the eye.
Place a ruler on the station point of the map and si^t it In the
direction of any object which it is desired to plot. Draw a line
along the edge of the ruler and on It lay off to the adopted scale the
distance of the object if known or assumed. When all the desired
azimuths have been taken from the station, sight the ruler to the
second station and draw its azimuth, and then proceed to that
station, pacing the distance. Arrived at the forward station, plot
the paced distance, orient the board over the station, and proceed as
before. If any of the objects taken at the first station can be seen
from the second, new azimuths mav be taken to them which will
locate them by intersection (fig. .24). If no compass is at hand,
orient the board arbitrarily at the first station, and at the second
station orient it by placing the ruler on the line between the two,
and sighting back to the station just left. Figure 25 shows the
relative positions of board and ground at four successive stations.
55. Traversinnr with sketching board. — The sketching board
(small planetable) is a compact device for traversing by the oriented-
map method. The compass is set into the board, and a movable
index is provided which can be revolved to place it parallel to the
assumed meridian on the map. When the needle is* brought parallel
to the. wire the board is oriented. The needle may be parallel to the
index wires, but end for end, or 180* out of its true position, in
which case the sketcher is turned completely around. Such a mis-
take is so great and so obvious that it needs no preventive, but a
sketcher may note at the outset whether the N or 8 end of the
EBcoirirAissAirGx.
47
0^
-vC^^J^^
c / -/' —
Flflr.24
-JF
Flff.25
Position at 04
Traversing by plane table and Resection
EnaiHEKB FISU) XAinTAL.
8 toward the stud-which moves the wlies and keep It In tbU
. _. ^..,tch[ng I oard .. ,
been distarded The dmlgn and plan of assigning tu"
0 the Bfiveral arMi of the service has oeeo approved by
y of War The outfit Is divided Into equipment, whleh It
and auppUea which are expendable The complete out
The tripod Is of wood with telescopln? less, which fold to 15 iDcben
or eitead to about 40 Inebes and detach from the top tor packing In
the container. The top, also of wood, In provided with a heavy
tbQmbscrew for nCtnchlns the board, and is covered wltb felt to give
_ a — ..,..._ without sticking o- '■'— — ~
BECOniAItaANCX.
EITQIRXZS FIELD UANnAL.
BECOHITAIEtBAVCS.
5T. A
foUo-nlns ■nbJeclBi
■nbJectBi
I, — Gradients, especially tbe Bteepeat ; width of roadwi
ath, kind. BDd eoDdltlon ot paFfiif; ; widtb and deplli
Boll; Band, da:/, or gravel ; Mud ol Iccces and wldtb iwtween them.
Ttie sketcb aboDld also stow wbere the road U In embaokmeat or
mttlDB; where wemnB can not double or paaa, and where toot troops
can not tnarfh along the side between the wagon track and the
material of
tee I, stone,
! Bridges).
regetatlon :
' polBODons
II ; general
or valleTs,
is to tbelr
DtersectlDg
I telephone
' elerators,
blacksmitii.
w distBDeea
i^ AJ^IUHIIBI^ ^OBCI
» -.. «^^ ,;r/«' ^,,»< .-r .ti'w r». ., r: ^^rxa. tie- ist taxi>s ~iuQt
; .►•'* '•,' " • .» ^•..^.--? -T r.rf.»r#t^; -.rr, lis- ar •«rtr!llrt^ *rT»i«. "te
/. y* »<"**♦'' "* ' ,- -o^xj ^ -I Aff « .Kjintitc ii*^^ "rv-TTnaiHllin:: .;rrnind
*'*' 'rt r''J''' » •♦• ■<♦''• I'' '>^ •^*J>nltP^ rf twiaMi^rTLr -^ ^^^^T^^I^ "an i^
.' ' v< < -i/^ '/ r.-?+ ^jv.f*"!! tn >r M^r miKa *«1 and
-'.« ^-".*A^*^'/ '»«-m ^^flrwrvrt 1^ titfft ^vaA .rtw •:».•«•«• r-^^ra^B -a* antt
,r j,>>\, , f .^ *»'.4.. '-♦ '•.vMmwTift V^jJ.Jt 7 tf vin'r suuuiic anif ftizui
^..r,,'/,..4 y ,/^ ///^v. SMfV ^f •t:**'* rr,'^Mi 3fo<#^ th* ««*r!: posrtiOB of
fff*^-, <v^'f ^ A M>»-ir4 ''►n V.fft hj^n»i« %y irh><i. rtK^y maj !ie found:
^^t*"^, P''(\^f^. ftf'^ fyft^'f* f>i iv^f v.rA ; T*irxity ^ <TOmp«t: posftlon
r^fA/.^, ^M*.' . *{/1j^ f/r (f^AMsut. tf.-^^A «V>-iM n/it be motv ttian 4 feet
F^'N^f/f hit f'tt7m\ti, %^ If-H U^ lf.f»Mrj, stnA 2 (tftt 4 inches for
if fff if./f t^t^tfo ihifUi-tf ^.r* n^t\,f^ «A »pc.r/»rfw!!f to bridees and
r//Mf^. ii\f\\h M fffnn^nv. nUtpn^, «//», HTe^rt of w^mtlicr and tTaAc.
M'^/a A-/fA'f*f|^ fM /j#r#riae)Mnf/ f/f fffi^g^ and fords.
I^fifhthm, htfniHt mm4 *fth^r m^Mm» ot ermmmlmm' — Position of
Ifniki ■fiiifthhfUfn $ufi jffnrnfnMUif fftr horses and loaded wagons:
'»'^^-' fmthif't. nttfi ti)inU of ^tffnfM: method of propalslon ; ^Ites for
hfUjhnj hti(fi(rn Of ft*ttif''^' /'tmrHHef of site for constmetion, uso,
Mofi ntfhfttthj iftn9Uo)if of U^nu^n And trJbutary streams; approaches
Hui] r^hifth or loutkA , ¥fUUU of rlvcf snd fnaximiim surface Telocity of
hut it-ill- u *ih*ntni tor Vtti I'ottntrwilon or repair of boats, bridges,
ht htiv-'*
flH«i«flHlli<ffS- t*^ni't^H ttuUiiUn for Inundations by damming or ob-
»I|(mIM)« m mmimiiv hi\tUti Hiino, or by cutting a leree or dike. Noto
{|ilM>.i| jh.tiJK MM uMMiMjl )lntil(i Id tmlursl or artlflclal Inundations and
M)M HMf»..«l |mmU III f»il|M«r liy known landmarks when the road Is
HujiiMtMil Sit iiMi^ittih^ litutidMllon 2 fi'M deep on level ground is
ri Hi-HnMrt HltqjiU'li* Mdluttn fhu I'oiulN iiF^^ vfry sound and marked by
hh»-'' l'H«|.i I'll liuni v^ht1u mo mitrkiMl a dip In the roadbed of 3
M( \ I >M( iHMv iMKiltM- ni»i iHmd tmimHsablo. A railroad bed Is soon
'Mt |ii>|(M«Mu«UaiiMMM« ur M riiMrofid. -The lln^. Local name :
MMulMM huhtU iMul «tUlHiu*«ti4 tH*tvvt'*»n stiittouH and other points ;
ttM>«h»'. »\\\*.\\\ \\\; \\\\\\\\\k\ ti'hi'HJ n»mlttlon of roadlKHl. ties, and rails:
(1*mHwu,»« .M\\l M.kUnhv u\ itvtM'ttowM v»r wnahouts: faculties for repair:
v*«H»lh«<*M \\\ \UM\ \,k\ \\,\\ t\iV \\\m\A\\\\& ti\Htp« aUmff the line.
» iM\M» l?i w»u| liv(«iii%»«iv NumlH^r ami location: dimensions;
hUs \\< \^\\\\\y^[ i\WA\\^ vvC iW«t(\»>lu)£ aiut rt^v^ilrlnjp: of blockini^
iMwyi *1*^^K. Nv»mt^v a>ut nature of w»s:ln^>« and cars arall-
, ^p>U\ uM l^*»»*is»»u»»»i ti\sMw tvtw^w iiWu p<4bIs: facilities
vwUsusiu, ^^mouM utUu>», ^^x x^vAiv r5<iK old binlWia.. etc; locm-
BEOOKHAlSSAirCB. Ik
Stattoiui. — Name and location; facilities for entrainlnisr and de-
training troops witti wagons and horses; platforms on through Itne
and sidings ; ramps ; sidetracks, number and capacity ; turntables ;
water tanks; fuel supply ; storage faculties; derricks or cranes;
cross-overs for teams and pedestrians. Facilities at hand for hos-
Sitals, camps, depots ; for feeding men, heating cofifee, watering horses
uring temporary belts.
Other comnmnlcatlons. — Telegraph lines ; number and location
of stations, nnmt>er of wires ; connections ; parallel highways, roads,
rivers, or canals ; means of access from same to railroad ; junctions
and crossings of other lines ; relative elevation ; facilities for laying
temporary switches and sidings at stations or between crossing lines.
Defenstbtltty^. — Heights commanding line of road ; defense of
stations ; defense of road and telegraph lines against raiding parties ;
structures exposed to demolition ; defense and attack of same ; defiles
and river crossings.
60. Reconnaissance of a wood or forest. — Note all roads
and paths, and all hills, . ravines, and streams within the wood or
skirting the edges ; kinds of trees, density and growth ; underbrush,
prevalence of poisonous shrubs and vines ; marshy or large open
spaces ; practicability of forming new roads by cutting ; creation of
obstacles by felling trees ; If there are no roads traverse the shortest
practicable path between the point of entrance and point of exit, and
mark bowlders or blaze trees, set stakes, or otherwise indicate this
path, and also give compass bearings of the route to be followed.
Note the exterior forms of the woods, whether parts of the edge
flank other parts ; connection with neighboring pieces of wood by
scattered trees or clearings ; undulations of the ground that would
give cover to attacking force or to defenders.
61. Reconnatssanee of mountains. — Note the number and
{>o8ltions of paspiei through the mountains, of roads and trails lead-
ng to these passes. th«r condition, practicability, and means of
repair ; steepness or slopes on the sides of roads : means of con-
structing additional roads ; watercourses, their direction, nature, and
time of floods ; means of crossing. Note ravines and open glades on
mountain sides, lookout points, and good signal stations; note time
and duration of snowdrifts on roads or passes ; depth of drifts and
possibility of removing them or of traveling on the surface of the
snow. Note extent and nature of forest growth.
62. Reconnaissance for a camp or winter quarters' —
Site. — Location, elevation, and area ; sanitary features, such as
dralna|;e» dryness, and general character of top soil ; proximity of
swampy ground or stagnant ponds.
Commnnications. — Sjifiiciency of existing roads and paths,
maximum grades, probable condition under heavy traffic and In bad
weather, location and kind of materials available for Improvement
or repair, railroad or water communication and terminal facilities
of same.
"Ww^t^r and fnel. — Location, kind, and quantity of fuel at hand ;
quality and quantity of water ; facilities for filling water carts, for
watering animals and for washing and bathing: nature of supply, as
wells, springs, running streams, and its reliability.
Shelter and conveniences. — Proximity of trees, brush, wood,
hay, and straw for huts and bedding ; of markets ; of towns and
Till Acres.
Dere'nslbillty-. — Location of outposts and guards ; location and
character of defensive positions in or near the camp ; force required
to hold positions which may command the camp.
63. Reconnaissance of a position. — This problem usually in-
cludes the selection of the position, and is therefore tactical as well
as topographical. Certain relations and conditions must be observed
in the selection, and the extent and degree in which they are found
must be clearly shown on the map or in the report.
The lenflTth of the positbn, or it£i development along the firln<»
line, should be proportional to the force available for its occupat^
M ENQINEBB FIBLB SCANTTAL.
Exact roles can not be given, bat 5»000 infantry per mile or 3 men
pel- yard 1b the nsual estimate.
Tbe flanks muat be secure. Impassable natural features, a
river, mountain, or stream form the best flank: Lacking these, a
wood, a deep ravine, a cliff, or a high hill will serve. Even with
these features absent a flank may be strengthened by the construc-
tion of a strong earthwork, but the general rule obtains that natural
weakness of the flanks must be made up by a greater number of men,
or by the substitution of cavalry for infantry in case the ground
favors the movements of mounted troops.
If the flanks are naturally stronar the line should be with-
drawn to make the entire position reentrant; if the fla»ks are
natnrally ^veak the connecting line should be held straight or
advanced so as to make the position straight or salient.
The #ent]i of tb.e position, or its extent in. rear of the firing
line, should afford natural cover for supports, reserves, and trains,
which may require a total depth of 800 to 2,400 yards, but a short
position may be relatively shallower than a long one. Three or four
parallel ridges, 300 to 600 yards apart, with the intervening ground
practicable, form an excellent position. If the first ridge is somewhat
higher than the rest, so much the better. Whatever cover there may
be for the component parts of the force, whether natural -or artificial,
fences, ditches, trees, etc., should be shown or described. If digging
is necessary, its amount and the character of the soil should be
stated.
8tron«r points in front of tbe line, which may be occupied
as outposts, should be shown.
Conunpnication sbonld be free in every direction, concealed
so far as possible from the enemy's view.
ArtUlerr positions are required when that arm is represented
in the occupying force, as will usuallv be the case. They shoald
permit the guns to sweep all ground m front of the position over
which the enemy can advance to the limit of effective range. Every
point in front of the position and within range which commands any
part of it is an element of weakness.
Ranges at which the enemy can be seen and reached by artHIery
fire; the points beyond rifle range covered by such fire and its
relative command of adverse artillery positions should be shown or
described.
If possible, similar information should be obtained of the ground
likely to be occupied by the enemy, in forming for attack or in
taking up a counter pomtion.
64. A position occupied by an eneniy must be reconnoitered
from a distance, and few details can actually be seen. Valuable in-
ferences may be drawn by remembering that the enemy has probably
chosen his position in accordance with the principles above given.
Especial attention should be given to the flanks and the feasibility
of turning one of them.
65. A position sketcb will usually be on a scale of 6 inches or
12 inches to the mile. It will be found most convenient * and ex-
? editions to make it by the compass and drawing-board method
par. 50) or the method with oriented board alone (par. 54). Tlxe
traverse will include the fewest points from which the entire area
can be seen, often only two, and all other features will be located
by intersections from these points. Elevations may be taken by
slope board or clinometer, the height of the first point ocenplc^ beiaar
arbitrarily assumed if not known.
If two points can be found which overlook the area is front of
them and which are also visible from each other, tbe con&pasa aaa^y
be dispensed witb except for a meridian. Measure the dist&nee
between the two points. Assume the position of one of the points
and mt the line joining them, so as to biing the desired area on tlie
paper. From the first point lay off on the line the distance between
the two points to tbe adopted scale and plot the second point. rFbe
KBCONITAISSANCB. W
line joining the two is called the 1»a«e, and will be near one edge
of the board if all the area to be mapped is on one side of the line
or toward the middle if it is on both sides.
Place the board over the first point; lay the ruler along the bate
and tnm the board until the ruler points to the second point. Keep
the board in this position and point the ruler successively to the
objects to be located, drawing the lines as explained in paragraph 64.
Gradients are written along the corresponding azimuths. One
gradient should be taken to each point determined.
Proceed to the second point. Lay the ruler along the base and
point it to the first point. Point the ruler to the objects to be
k>cated, marking where it crosses the line to the same object drawn
from the first point.
66. Contouring is a method of exhibiting relief of ground by
means of lines so drawn on a map as to indicate points of equal
elevation. The lines so drawn on a map and the corresponding lines
on the ground are called contours. The word contouring is applied
to the fieldwork directed especially to obtaining data for drawing
contours.
The difference of elevation of points in adjacent contours is called
the contour Interval, and is usually constant for all the contours
on the same map. The horizontal distance between contours, meas-
ured in a radial direction with reference to the curvature of the
contours will be referred to as contour distance.
The theory of contouring is that no inadmissible error will be
made by supposing the slope of the ground from a point in one
contour to the corresponding point in the next, or along the contour
distance, to be a straight line. The less the contour interval, the
less error will be made. If in figure 28 the curved line AB represents
the actual surface of the ground, and points 1, 3, 5, the elevation
of successive contours, the broken line 1, 8, . 5, will represent the
assumed ground surface, and its departure from the line AB is the
error introduced. If now the points 2, 4, and 6 are also determined,
or the contour intervals be reduced one-half, the assumed slope is 1,
2, 3, 4, 5, 6, which differs less from the line AB than the line 1, 8, 5,
and hence introduces less error. With points determined at very
short intervals the error is practically eliminated.
If contour distances decreaae with elevation,, or the contours
become closer as they go higher, the slope is concave, and points
between contours are lower than the straight line joining correspond-
ing contour points. If the contours become closer as the ground falls,
the ground is convex, or lies above the straight line joining cor-
responding contour points. A point of inflection, or change from
convex to concave, is at the point where the contour distance is less
or greater than those on either side of it. Bqual contour distances
correspond to uniform slope.
67. One contour does not necessarily join all the points of the same
elevation on the map but only those which have a continuous series
of points of the same elevation joining them. It may require several
contours to take in all the points of a given elevation on the map.
Parts of the same contour will appear a^ separate when the ground
over which they could be connected is not on the map. The selection
of the points to connect in one contour is the diflScult part of the
process and can not be done correctly without thorough knowledge
of the principles of the method and a good idea of the general shape
of the ground to be cohtoured. In military reconnaissance only
enough elevations can usually be taken in the field to guide one
who has seen and studied the ground in drawing the contours. No
one who has not seen and studied the ground should be expected or
permitted to draw contours from such data. Brroneous information
may be worse than none at all.
68. For equal contour intervals the map contours are closer to-
gether as the slope is steeper. It follows that for steep slopes the
map contours will approach each other very closely, and for a ver-
tical wall or cliff they will coincide.
EiraDTEIS SfKLD TUSVAL.
Esiry contour must cloae upon Itself In a loop or else muit eitend
nnbroken (rom one point on the margin on the map to aome other
^..^. ,_ .V„ 7.. .^ ., _ ,, _,.,.. 1_ .Ig p^gg gf ]jfgg
iRtream until It
he<l, the contour
l9 tbat of the
go Id pairs. A
■till loner It
a datam plane.
Ic scale ia aeed.
Igures at points
Ite the D umbers
s sboatd alirars
: b; flxlQC the extreme point
71. Looking at contours t
those coDcave to the obserr
Tallers hre also lines o( drali
to aetermlne a waty contonr will He on ijcaiiu„.
rivers, creeks, brooks, aod rlTnlets, aad b; cavlneB, or other depres-
ralnage line jrowa leas In the direction of flow.
OQB dry at most si
The slop
Tributaries.
Ihelr Junction, and also Increase In slope toward their Eource
enlly. In a limited area, the sources will be at ceai-l; the s. ...
ration. To apply thla principle In Increasing the amount of topo-
graphical relief that ma; legiamatelr be drawn from a given numSer
of known elevations, let Ssure 33 represent the drainage lines of ao
area taken from a ctiil map. Suppose the ground to have been studied
ud elevations to have been determined at 2 points, A and B. How
Bocta topography can be drawn?
The 110-foot contour will be above the 10,'i-foot and by a distance
jomewhat leaa than I he lenjjth AB, because the slope becomes steeper
■ad the contour distance less In going upstream. The succeeding con-
lonrs at 10-foot intervals will cross the tributary at gnidually decreaa-
lag distances, as lnd'-~— ' --- ' '" "■" — """ ■^'•" "" '-
found to be about 13i
and draw tlie contoL. _. ,
where It crosses the streams, and that the part ui-iween me 5
oHivei and advanced. Lay off the contour points on the otb<
lines, keeping in mind the law of slopes, and draw the Other
followUiK the same rule aa for the Orst
r
68
ENGINEEK FIELD JCANTTAL.
Fl8r.83
/y
^'
f
k
V M 63 B2 n tW «
^ ij 53 / k 53 s/ fit
FIST. 84
BEoomAnsAscB. m
I cnoagb •levatloos wer« taken on Btiwm llneB the cone^Te
. .V. — . — -j, ^ould be laltl; well determlaed. but tbe convei
- '- ^»^t uncertain. It Lb known that t&ey are
~" " " " rmatlon Is supplied
Blope board. It a
,r.".
at tbe lallent
ridge I be noted wbenever
It _... r . traverse the ridge
lines mnit be run out. The; must be coaDectF^d In plan (dlBtance and
■ilniatb) and In elevation wltb the drainage llnea. when drainage
and tidge Ilnee are plotted on tbe map the contour points, If not aeta-
allv observed, maj be Interpolated and the coniours drawn.
The aymmeti7 of adjacent cuntours is obTloua from tbe Innpeetlon
of any coDtoared mail, and ttila relation may be utlllied where one
contour lias been well determined, to draw the one on either aide of it
from a rery few points, ofteu but one. If the contours are war; tbej
wUl generallj be a little farther apart at the concav and coDvez
points than at the reversion points between them. If the Mntoura Me
Dot WBvy they are generally parallel.
74. If tbe relief ot the ground Is bo allKkt that the drainage
and ridge lines are uncertain the field wort of contouring is b^
done by taking elevations at points arbitrarily selected. Such points
will osnally be In straight lines running In tbe general direction
of the steepest slope. Tbe points are plotted on the map, the cor-
responding elevations written near them, and the con too rg are
Interpolated as Indicated In figure 34, Bssumlng that the snrface of
the ground between observed points is a straight line. The closer
the points are together the less error Is Involved In tbls assumption.
If the conntr; IB comparatively fiat and unbroken, profiles may
be ran along roads and paths and conloure sketched In on each
■Ide so far as they can be seen. Then by going over the Intervening
ironnd and observing Its shape, the portions drawn can be Joined with
ihe eye with Bnffldent accuracy.
In towns and villages profiles along Intersecting streets and the
Btndy ot the Interrenlng space fumiBb data for approximate eon-
75. Sloi^ e^nlvalenta. — Actual distances between contours on a
map depend on the contoar Interval, the scale of the map, and the
graillenL For any given map tbe contour Interval and scale ar«
coDBtsnt, and the distances between contours depend on tbe slope
■lone. On any map with oontonrs at eqaal Intervals each gradient
has Its corresponding contour distance, which is called Its e<iBl*>-
62 ENaOTESR PISLD KAHTTAL.
mounted can cover 15 miles a day steadily, or in an emergency 20
or 25, and can keep up with infantry on a forced march or with cav-
alry marching at ordinary rate.
The reconnaissance for a column should include besides the road
traveled the nearest parallel road on each side and all connecting
roads ' between them. Each mile traversed by the column on the
main road will thus involve 2i to 5 miles of sketching.
If a reconnaissance is to be made when a force is not in motion,
the area to be covered will usually be so large and the time allowed
so short as to make it necessary to combine the work of a number
of sketchers.
78. If any map !■ available, the area to be reconnoitered should
be outlined on it and subdivided into as many parts as there are
sketchers, the parts to be made equal, not in size necessarily, but in
amount of work and time required, the important point being that
all the parts shall be finished at the same hour.
Each of these parts is assigned to a sketcher, with full instmc-
tions as to the amount and class of work to be done, the scale to be
used — which should be the same for all — ^and the place and hour at
which the sketch must be turned In. If practicable, each sketcher
should be given a tracing or copy of enough of the map to show the
boundaries of his own task and the adjacent features of those next
to his.
If there is no map, the area may be indicated by landmarks, but
it will be usually necessary, and always desirable, to go over the
ground and point out his task to each sketcher. when boundaries
are definite there need be very little overlapping. The amount of
reduplication must increase as boundaries become more vague.
79. The area to be mapped may be divided up in any convenient
way, but it is best to use roads, fences, streams, or other well-defined
lines as much as possible. Lacking these, compass courses passins^
through well-defined points will answer.
In a road sketch one man should be assigned to the main road or
that on which the column is marching. Others will be assigned to
such parallel and intersecting roads as it may be necessary to map.
So far as practicable, side parties should leave the main road by an
intersecting road, traverse a short stretch of parallel road, and
return to the main road by another cross road.
80. Compilation — The sketches when turned in are consolidated,
usually by pasting them in their proper relative positions on a larg:e
sheet of paper, or else by pasting them together at their edges so
that corresponding features will Join. If one of them does not ex-
actly fit, as will often happen, the adjustment is best made by cut-
ting the sketch into two or more pieces and movlngthem with respect
to each other so as to absorb the discrepancy. Thus, if a piece of
road is half an inch too short, cut it at three or four places on lines
peri>endicular to the road and separate the pieces by a sixth or
eighth of an inch. If too long, overlap the pieces instead of sepa-
rating them. If a road or other feature is out of azimuth, make a
cut through one of its ends and swing it into place. These opera^
tions may be combined. The adjustment is rapid and sufilciently
exact. If a sketch is too much out -to be adjusted by this process,
it will usually be of little value and time will be saved by leavina
it out of the compilation and filling in the gap free-hand, nsins the
sketch as a sruide
Figure 88 illustrates this method of adjustment.
81. Reproduction. — As many copies of the map will be made as
circumstances may require. The first step is to divide the map into
sections of convenient and usually equal size, and make a tracing of
each. The size of the sections will usually be determined by the
method of reproduction to be used and the size of the apparatus at
hand. Time will be saved If there are not more sections than there
are men available to trace, supposing that all the tracers are of ap-
proximately the same speed. If one of them can won two or three
EECONHAISSANCE.
Fig. 88
64 siranrBBB viez.ii ieakttal.
times as fast as the average, two or more sections should be re-
served for him. the idea being that the work will be done in the
shortest time if so arranged that all finish at once.
With fairlv expert sketchers, it will be possible to have each Ink
his work before turning it in. A useful expedient in case of great
haste is to make the sketches themselves transparent by oiling and
fasten them together for use instead of a tracing.
82. The tracing made, further processes depend upon the time
available and whether the work can be done in daylight or must be
done at night.
Of processes requiring sunlight, the most reliable, simplest, and
quickest is the blue-print proc«iis.
The prepared paper may be purchased in rolls of 10 or 50 yards.
It should be put up in tin foil and each 6 or 8 rolls should be in a
sealed tin case ; it will then keep in good condition for a long time.
If necessary to sensitize the paper in the field the following solu-
tions must be prepared :
Ouncea.
Stock solution A f^^^^%f ^^ i***^^ "^.^°''!!!*'!.z::'::::: I
stock solution B {wftir?![*^^^^^^ I
For use mix 4 parts of A with 3 parts of B.
Unprepared paper may be purchased in 50-yard rolls. To sensitise
the paper a sheet of the desired siaw ife cut from the roll and placed
on a nat surface ; the mixed solution is applied with a sponge to
the upper surface in a smooth, even coat, care being taken not to
wet through to the back of the paper. The sheet is hung up in a
dark room until dry, when it is ready for use. Only enough paper
for a day's use is sensitized at one time, for it does not keep well.
The exposure takes from four to eight minutes in bright sunl'ght.
varying with the intensity of the light and the transparency of the
tracing. Under other conditions than sunlight a much longer ex-
posure is required ; sometimes an hour or more. Care must be taken
that : the paper is not taken from the frame before it has been sulB-
ciently exposed. When the margin protruding from under the trac-
ing has a greenish-bronze color, open one part of the back of the
frame and observe the print. The lines should stand out sliarp and
distinct on a gray background. Take the print from the frame and
Slace it in a tray containing water sufficient to fully cover the print.
^inse it until the lines stand out in clear white, then hang up to
dry. It is to be remembered that the fresher the paper is the slower
it will print and the quicker it will wash out : the older the paper is
the quicker it will print but the slower it will wash.
Additions and alterations may be made to blue prints with a lO
per cent solution of oxalate of potash used as an ink. If it shows a
tendency to run, add a very little mucilage. Common soda may be
usedi but the lines have a yellowish cast instead of the pure white
which the potash gives. Additions and alterations of a drawing are
conveniently made by inking the lines of a blue print with water-
proof liquid India ink and removing all the blue color by the potash
or soda solutions. The black lines then remain on a white ground.
They take well in photographing, and by treating the paper with
oil, it becomes transparent enough for contact printing, being used in
place of a tracing and in the same way.
Brown prints. — Next in point of simplicity for daylight use is
the brown-prSnt procesii. It is in many respects the most satis-
factory of the copying processes. The paper is purchased pre-
pared.
After exposure for about two minutes in bright sunlight the margin
protruding from under the tracing turns from its original ligrht
yellow to a reddish-brown color. The print is tlien tak^i from the
frame, immersed in water, and thoroughly rinsed on t>oth sides,
when the lines come out in perfect white on a sepia-brown ground.
EECOKKAISSAHCE. 66
It is then immersed in a fixing bath made from the salt which ac-
companies each roll of the paper (2 ounces of fixing salt to 1 gallon
of water) ; this makes the print permanent and also darkens the
sepia-brown color, the lines remaining white. After fixing the print
must be thoroughly washed for 20 to 30 minutes and then hung up
to dry.
The brown color being impervious to light makes this paper very
valuable for negatives which may be used to produce positive copies,
either with the blue or brown print papers, yielding an exact repro-
duction of the original in either blue or brown lines on a white
background. In making the positive prints from the brown-paper
n^atives the time of exposure is somewhat longer, since the brown-
Srocess paper is not as transparent as tracing cloth or tracing paper.
Sven very fine lines of the original are reproduced with surprising
distinctness, due to the fact that in both manipulations the orgiinal
is in direct contact with the sensitive side of the paper, so that no
light can enter sideways under the lines.
By making several negatives and printing from them simultaneously
the rate of reproduction may be largely increased.
83. For printUiflT hy artificial liipht bromide papers are used.
A contact print from the tracing has clear white lines on a very
dark-brown ground. The contrast is clear and agreeable. Altera-
tions mav be made with a sharp red pencil, which makes a legible
line, or by scratching through the emulsion, which makes a white
line. A print can be obtained quickly from the light of three candles
at 12 inches distance.
To develop broBoiide prints make a stock solution of hydro-
diinon, 150 gr. ; sodium sulphite, 360 gr. ; water, 12 ob.
For use, to 1 oz. of stock solution add 1 dr. rodinal and 8 oz.
water ; or, make stock solution of metol, 150 gr. ; sodium sulphite
crystals, 2^ oz. ; sodium carbonate crystals, 3i oz. ; bromide potash,
8 gr. ; water, 20 oz. For use, add 1 oz. stock solution to 4 oz. water.
Acetic acid is used to clear bromide prints after development and
to stop the action of the developer, IB oz. water to 1 dr. acetic acid.
For flxinsT bromide prints use hyposulphite of soda, 1 oz. ;
water, 6 oz. A little alum added to the fixing bath in hot weather
hardens the film.
A bromide print may be made transparent by oil and used for
contact printing by artificial light. It will be better, though not
essential, to secure a paper for negatives thinner than that usually
Bupidled for prints.
The C9^cle of operations for quick reproduction by the bromide
process is as follows :
From a tracing or transparent drawing make, say, 3 to 5 negatives.
Make them transparent and start printing from ali of them. If the
sketchers are in by 5.30 p. m., the negatives can be ready for printing
by 7 p. m., and after that prints can be turned out at the rate of
15 per hour from each negative. It should not be difficult to have
all that are needed for the next day done by M p. m.
84. Transfer processes. — -With tbe hectoflrraph the drawing
is made In a special ink and pressed face down on the surface of a
gelatin compound in a metal pan. When the paper is pulled off the
drawing appears reversed on the gelatin surface. A piece of blank
paper pressed on the surface and then withdrawn shows the drawing
direct in purplish lines. Fifty to 100 impressions may be taken.
Each print is covered with a thin film of the compound and is sticky,
curly, and very stubborn. The process is at best only a makeshift,
but it is the easiest of all to improvise and the simplest to operate.
For quick work several pans should be provided, as each must be
washed after use and should not be used again until well dried.
The hectograph compound is made of — Parts.
Glue or gelatin 100
Glycerin , 400
Water 400
04346"— 17 5
86 ENGINEEE FIELD HANTJAL.
Kaolin, 50 parts, or some fine inert light-colored powder may be
added with advantage. The ingredients require prolonged mixing
at 200" F., which is best obtaised in a salt-water bath, 2 ounces
salt to 1 pint water.
The ink is made of— Paris.
Nigrosine black 1
Glycerin 4
Water 14
Writing or drawing is done with a fresh, clean steel pen. The sur-
face of the compound is moistened lightly with a brush or sponge and
allowed to nearly dry, when the copy is laid smoothly on face down
and rubbed to a good contact throughout, eliminating all air bubbles.
The paper is allowed remain two or three minutes and then removed
by starting one corner and pulling parallel to the surface. The sheets
for impressions are put on and removed In the same way, except that
they are left on but few seconds.
With the black aatocopyist the drawing is made in a special
ink and transferred to a parchment sheet held in a special frame;
This process is free from some of the objections to the hectograph,
but it is more difiScult to work. The copies are in printer's ink, are
permanent, and very satisfactory.
85. Landmcape sketch tnff. — Free-hand sketching can not take
the place of topography, but it is a valuable adjunct and should be
practiced by every soldier who has any aptitude for pictorial drawing.
A sketch differs from a photograph only In that it shows in sharp
outline a limited number of the larger and characteristic features
easily seen and understood, while the photograph shows all details,
many of them so minute that they are lost in a mass of confused
forms, with the form lines, other than the sky line, relatively incon-
spicuous. All the lines of a perfect sketch exist in a photograph, bat
close scinitiny is often necessary to find them. If sought out and
traced, however, a perfect sketch results. Tracing from photographs
is excellent practice.
The ontflt for field sketching should be as simple as possible. A
sketchbook with a canvas cover, carried in a water-tight case, to-
;?ether with a few lead pencils B, F, and H, and pieces of soft and
hard rubber are the essentials for satisfactory work. For active field
work the book should be no wider than can be carried in the pocket
of a service blouse and relatively long, say 5 by 9 inches.
The point of vle'w should as a rule be high enough to give a com-
prehensive grasp of all that is important — a rock, a knoll, a hill, a
peak — depending upon the conditions. Face toward the middle of the
field of view which is determined upon. Hold the board or sketchbook
vertically before the eye and move it backward or forward until the
sheet just fills the field. Lower the board until the sky line of the
hills can be seen above its top edge, and with a pencil mark on that
edge the points corresponding to the principal salients and reentrants
of the hill forms. If desirable the board can ,be moved sideways far
enough to enable the principal heights and depressions to be marked
on the vertical edge. By intersecting references the locations can
then be easily established on the sheet. From these points the forms
can be sketched in with much greater accuracy.
Proceed next to draw the hills in outline, out faintly, with atten-
tion to the larger curves or humps at first. Go over them again
with more care, bringing out the small irregularities. If any part
of the horizon Is visible, draw In lightly, and then complete the gen-
eral mass of hills by drawing the water or base lines. Seek now for
the surface character of the hills by tracing the ravine lines. The
knobs and foothills are brought out by tracing the tree meanders
that show form. All changes in form or breaks in the ground produce
corresponding breaks In the foliage of the tree masses, which show
in the distance as irregular lines. If the more important of these
are sought and drawn, the general character of the hill will result.
AxoonrAXSsjarox. ev
Add now the foreground crest, and the skeleton of the sketch is com-
plete.
The road and railroad meanders should follow as a rule, and the
fences of the fields. Cultivate^ land is rendered by parallel irregu-
larly broken lines. Houses, fortifications, trenches^ etc., will be drawn
more or less in detail according to distance and importance. Enemy's
lines or trenches even at a greater distance should be strongly marked
by simple black lines. The indication of forests and trees is the most
difficult feature for students. The indications given in the accom-
panying sketches will show the treatment in outline work.
Figures 89 and 40 show a variety of forms sufficient for most
localities.
86. Hydrography. — Depth of water and character of bottom are
determined by sounding with a pole or with a lead and line. The
Monndins pole may be improvised, or of permanent form. A con-
venient one is 10 feet long, octagonal in section, tapering slightly
from middle to ends, diyided into feet which are painted alternately
white, and black or red. There should be an iron shoe at the bottom,
heavy enough to make the rod stand erect when free in deep water.
Such a rod is convenient to nse in water 9 feet or less in depth.
If a sounding lead is not furnished, any compact weight may be
used. The ■onndinff line should be of braided hemp or cotton,
I to i inch in diameter, and tagged with cloth or leather. The tag-
ging will depend on the depth to be measured and degree of precision
required. Cloth of different colors may be used for different units,
and leatiier tags may be distinguished by cutting notches or punching
holes in them. The line should be thoroughly wet, stretched, and
allowed to dry. It eliould then be wet again and tagged while wet.
The zero of the graduation is at the bottom of the lead or weight.
A lead and line are best connected by a rawhide thong passing
through an eye in the lead and an eye made in the end of the line.
Soundings* are usually referred to a plane parallel to the water sur-
face, horizontal except in flowing streams. The plane usually selected
is the water surface itself if stationary, or one of its positions if
variable, so that soundings will indicate approximately the actual
depths of water. The elevation ot the water surface in the position
selected is called the datum l^>el. If the surface elevation varies,
a gange rod must be set near the water's edge, and read often enough
to plot a continuous curve of water level. The time of beginning and
enoing a particular group of soundings is noted. The mean elevation
of the water surface during that interval is taken from the curve,
and the soundings are corrected by the difference between the actual
level and the datum level. If the correction to be applied is less than
half a foot, it is usually neglected.
The material of the bottom, as rock, gravel, sand, or mud, can usu-
ally be told from the feeling of the rod or lead when it strikes. A
specimen of the bottom can be brought up by smearing the end of the
lead with tallow.
A correct sounding is obtained only when the line or rod is plumb
and strai^t and its length correct, or its error known and applied.
Except for blunders in reading the line, only one source of error
operates to make the soundings too small, and that is a line which
has stretched since it was tagged or is too long. All other sources
of error make the soundings too large, and hence they are apt to be
80, and actual depths slightly less than those recorded will usually be
found.
To get a plumb sounding from a boat moving through the water,
the lead is thrown out or the pole inclined in the direction of motion
far enough to allow it to reach bottom by the time the boat is directly
over the spot where it strikes. Soundings taken with a line from a
moving boat will always be too large.
The most accurate soundings with lead and line in running water
are taken from a boat floating with the current, with line allowed to
68
ENOnrEEK FIELD KAHTTAL.
CO
KXOOBSAIBBAaCK.
EKGDTBEK FIELD lUHUAL.
rallied only a foot or ao betweeo
87. Loutian u(%oiindiiiK'' — Tlie Simplest method Is bj two .
IQBDt <rtll
tDstTDcted to keep tte flags In range'. oSlj one Instrument ana ob-
tor all work where the souniilngs can be taken In straight lines. Lo-
eHllOBD mej be maile from the bont b; two obBerverB taking
HlmnltajieauB compasB bearings to two known points on shore — see
resection — or by two simultaneous sextant anglps. The latter Is leas
convenient, as a special protractor Is required for rapid plotting.
map or chart contalnlDg souDdiDgs : " Soundings are In feet (or
meters) and are referred to the stage of water at (location of gauge)
at ^— o'clock, on the — day of — — . The elevation of flUs
datum level la —— feet (or meters)." If the reference plane Is ID-
dlned. add : " and Its Inclination ts ■ ■- ■ - In a — direction."
The first blank is filled with Che rate of fall eipreSBed In any recog-
nised WBj, and the second with a compass bearing.
S9. Hap TMdlDar Is esBentlally the reverse of map making. In
the latter proceaa gronnd Is measured and studied with a view ofform-
InK a mental plctnre of how a map ol It will look. In tb« former —
map reading — a map Is mi-asured and studied for the purpose' of form-
ing a mental picture of how the ground Itself looks. All rules and
piTuclptes beretofore stated as to rplatlons between ground and map
■re to be ased In studying the relations of map to ground.
The following snggeBtlous will aid the beginner :
Nste the mcFldlsii on the map and associate it in the mind with
the local meridian. This may be done by turning the map so that the
meridian will point to the north, using the compass as a guide It nec-
eesarv. If there la no meridian on the map look for Indications of
dli«ctlon In local names, or for some road, stream, rldge, or other
feature the general direction of which IB known.
Hote tke scale of the map. Estimate certain distances, as the
total wldtl ' length or distance between prominent points and
teat tbese ' by scaling. It there la no scale look for some in-
dlcatlcHiB c «. It may possibly be found in local names, as
Three UUe [Vo Mile House, etc. ; roads uniformly spaced, as
the United tnd surveys; city blocks, which are usually about
IDO tarda horter side ; railroad stations or sidings, the dis-
taoee of w be taken from time tables. If the map has par-
allels of la good scale may be drawn by assuming 69 miles to
each degre<, miles to each minute. It the ground is acceBslble
take two convenient points shown on the map and measure the dis-
tance between tbem.
If the map is conto
scale of slope equitalents. ._ —
which are the high and which the low 01
more likely to be elevstlone than depret . ^-^ .,
concentric, A single closed contour may be uncerlaln. Look for Indi-
cations of marsh or water Inside of It. It the contour Interval Is not
given It will be dlilicult to get any clue to it unless isolated elevatlona
appear on the map. If the ground Is accessible the contour Interval
may be determined by actual measurement of a gradient.
Rote all topograph li'sl and cultural signa and associate them In
mind with their advantages or disadvantages for military operaHooa.
"1, A problem frequently arising in map reading la that of de-
termining wbat palntu are vliilble from a fflvei
. ,.™., t,Q j[|(, gradient to It, if rising, Is gn
han the gradient to any Intermediate |
son gradients Bre conveniently repres —
e In feet divided by the difference ol elt
lint la visible when the gradient to It, if rising, Is greater, aod,
lllng. Is smaller than the gradient to any Intermediate point.
For this comparison gradients sre conveniently represented hy t
REGOHITIISSAKOX. 71
feet. The point will be visible when this quotient is smaller, if rising,
and larger, if falling, than the quotient for the intermediate point.
Thus, to determine whether the bridge near the Frenchman's (fig. 41)
is visible from Atchison Hill or is concealed by intermediate ground,
assume the highest point of Atchison Hill to be in the center of the
1,040 contour and to have an elevation of 1,050. The distance from
this point to the bridge is 5,610 feet, fall 250 feet, quotient 22.4. The
line of sight from this point to the bridge crosses the 960-foot contour
on the flank of Sentinel Hill at 8,060 feet distance, fall 90 feet, quo-
tient 34 ; hence bridge is not visible from Atchison Hill, since the
gradient is falling and the nearer point has the larger quotient.
Working from the bridge the quotient for the whole distance is 22.4,
as before, but the gradient is rising. The distance from the bridge to
the high point is 2,550 feet, rising ; difference of elevation 160 feet,
quotient 16; hence, as before, the top of Atchison Hill is not visible
from the bridge, since the gradient is rising and the nearer point has
the smaller quotient.
If one gradient is rising and the other falling, no computation is
necessary. A point of rising gradient will hide a farther point of fall-
ing gradient but will not be hidden by a nearer one.
91. Dravtringr. — ^The essential requirements of a good topographi-
cal drawing are accuracy and clearness. By accuracy is meant a
faithful exhibit of measurements and observations made in the field,
or of data taken from other maps. Clearness Involves absence of con-
fusion or crowding, and neatness in execution. Beauty and pic-
torial effect are obtainable by skilled draftsmen only, and while
always desirable are rarely necessary. Persons who are not skilled
draftsmen should not attempt pictorial effect, as it will detract from
accuracy and clearness without substituting anything of equal value.
A-vold nnnecesBary haste In plotting and drawing. If possible,
take time to check carefully all azimuths and distances plotted and
be sure they are exact. There should be no approximation on the
drawing board. Although an observer may have simply guessed
a distance to be 550 yards In the absence of other information the
plotter should be careful to lay it down at exactly 550 yards.
Start with clean paper and keep it as clean as possible. In the otRce
wipe off the instruments before using, especially rulers, scales, and
triangles. Dust the drawing carefully before beginning work. Dust
again when stopping and cover with a cloth or paper. If necessary,
dust the drawing and wash the hands occasionally while at work.
Malce all inik lines ilrni and Tery black. A drawing to be
made in ink is usually drawn first in pencil, and in such cases a
very hard pencil (4H or 6H) is best. If the pencil drawing is to
be traced a softer and blacker pencil should be used, but must be
kept well pointed.
India ink in stick form gives the best results, but the time re-
quired for proper grinding precludes its extensive use in military
field work. The prepared Inma inks In liquid form are ready for use
and are satisfactory. They must be kept well corked when not
actually filling a pen. If the ink gets thick in the bottle so that it
will not run freely from a fesh-filled pen add a little water.
The imlinff, or riffht-line pen (figs. 42 and 43) is best for
making lines, of uniform thickness. The points must be kept clean,
and when worn must be ground on a very fine stone to the form
shown and to exactly equal length. The points may be closed and
the ends shaped together, which will make them Identical. Then
open the points and grind each on thf» outside to a proper edge.
Right-line pens are set to make lines of different thicknesses by the
screw D, but the range for any one pen is limited, and different sizes
of pens are made. A very fine line can not be made with a coarse
pen, and it is difficult to make a very broad line with a fine one.
The points should never touch. If a line made with the points
slightly separated Is too coarse, take a smaller pen. These pens are
graded by the length over all. Five Inches is a medium and useful
size.
ENfilNEES STELD KUTUAI..
KECOHVAIBSAHOX.
74 ENGINBEll ITEID KAHTTAL.
Right-line pens may be filled by dipping an ordinary pen in the ink
and inserting it between the points. A strip of paper closely folded
may be usedf in the same way. In the bottle of prepared ink the
cork carries a small quill for filling. Take only as much ink as can
be used In two or three minutes. As soon as the fiow becomes the
least sluggish, the pen should be emptied and refilled. To empty or
clean the pen pass a piece of paper (the corner of a blotter is ex-
cellent) between the points.
Tlie adjustingr scre^w should not 1>e disturbed while work-
ing on lines of the same thickness. When changing from one thick-
ness to another, open the pen and clean more thoroughly. To reset
for a given thickness draw a short length on a scrap of paper and
lay it alonside of a line of the desired thickness, preyiously drawn.
The difference will be seen, the pen can be changed and another
trial made, and so on until the lines are matched.
For ruled lines the ruler or curve is laid in the proper position
and the pen drawn along the edge, lightly pressing against it. The
pen should be held with the plane of its points perpendicular to the
plane of the paper and in the direction of motion. The handle should
be slightly inclined in the same direction. For free-hand lines, as
contours, hold the pen in the same way and move the hand so as
to cause the points to follow the line.
In ruling with a writing pen choose one of a size which will make
a line of the required thickness without pressing on the paper. Dip
the point only in the ink. If the ruler has a beveled edge place it
with the top projecting. A curve or a ruler not beveled should be
raised slightly from the paper. The pen should not be inked al>ove
the point which touches the ruler. It is held as described for the
ruling pen. Parallel lines close together may be drawn with one
setting of the ruler by inclining the pen slightly.
Writing pens are best for stream lines. When it can be done, vary
the size of the pen to suit the thickness of line. When using a
writing pen free-hand do as much of the work as possible by draw-
ing the pen toward the body in about the direction of the down
stroke in writing.
For lettering* signs, and all free-hand work with the writing pen,
keep the pen clean and freshly inked and the ink free from dust and
of proper consistency to flow freely without dripping from the pen
in blots.
In using a circular pen (fig. 43), set the legs of the compasses so
that they will span the right distance and the pen point will be
vertical. The lead of a pencil point should be sharpened to the
shape of the ruling-pen points with the fiat side toward the pivot lesr
of the compasses. When using compasses with pen or pencil, incline
them slightly in the direction of motion and rotate the head between
the thumb and forefinger. Very slight pressure only should be nec-
essary beyond the weight of the instrument.
Figure 46 represents the most convenient instrument for measur-
ing the length of curved or broken lines on a map. The small wheel
is run over the line, and its length in the unit of the instrument is
read from the dial. This length is converted into actual length by
the scale of the map.
92. Papers. — Manila paper of cream or buff tint, usually called
detail paper, is suitable for sketches and drawings which are to be
traced or used in the field. Only the better grade stands erasing
and that ii;nperfectly. This paper comes in rolls 36, 42, and 54
inches wide. It may be ordered by the pound or yard.
White drawing paper may be had in rolls or sheets mounted on
muslin or unmounted. Whatman's cold-pressed fine-grain is most
generally useful. It comes in sheets of names and sizes as follows :
Royal, 19 by 24 inches ; Imperial, 22 by 30 inches : Double Elephant.
27 by 40 inches ; Antiquarian, 31 by 53 inches. Roll papers are 27
to 63 inches wide.
Sheet papers unmounted and kept fiat are best for field topo-
graphical use.
WORKS AN* STRUCTUnCS
DBuUtTndi -
h Ifacw ilMrfar SfraM
Tunnal ,
XaSlTMi Station of May klitd
Ahngroad
T^tgr^h LiM
Ahagtna
Elaatric flower Traaemiision Line
WORKS AND STRUCTURES
Tnat i tf, W
F«M ~
3 STRifCTURES
BaikSagK ID goiwal f"
Ruins -
CAvrcA _
HeapiUJ - - _ ..-.
Scboolbaiae _
Po^ Office
ToSt^aph Officm
CHy. Tawn. or Villag*
CHy, Town, or ViOugm (£»m
WORKS AND STRUCTURES
Cemetery
C£M ' '-f '
Mine or Quarry of any kind {or open cut) *
Prospect - - X
Simft
hfine Tunnel l'^'"'"^ -
[Showmg direction.
on Wells
Oil Tanks UbbrtviMUon OT)
Ooke Ovens
/:
F«nc« •/ any kind > .
(or b0Mrd ftnoti)
Stone
Fences < Worm
Wire
Hedge
\
W ;■■>—*——»»•«
Btrbmd Smooth
x—*— y— »— »-' o— •— a— ©-o
fj •; 1- .v^ ■- ., )» <i.-5 4^ 7> .^^
Fig. 61
BOUNDARIES, MA^nCS. AMO MONUMENTS
NiUwiMl, StMte» or Province Lino
County Line „ „
CivH TownMhip, Dietriet,
Prooinot, or Barrio
Reoervmtiwi Line
Lend-Oruit Line ,
City, VSk^, or Bormt^
Cemtftery^ Smell Perk, eta.
> ■ • ' ■> * I
Township, Section, end Quertm' Section
Linee iuy om for towuMpHee eloa; uk»
two for towntUp antf ooedoe Ham
\-
Townsiup end Seoticn Cornere Reoevered^^ ^ ^~
Boundary Monument % .
Trienguletion Station
Benohmerk V*
1232
U. S, Minerel Monument
Fig.-«2
ORAINAGK
Streams in general
Intermittent Streams
Lake or Pond in genersi -
(wth or without tint, wat^rJinkig,. «<c.)
Sah Pond (brokoa 9honmm^m»nmmt^
Jotbertoitteiii LjsJdb ^r Amtf .
Spring
Fans and Rapids.
*«^A--*Tw^*.- -•.^T**^- '9"---il^- V^*y.t'
.^
/
Glaeiers <
Contonn -
(or $s bohw)
Form UaoM showing flow.
Fig. M
N
( Showa by eealoiirt. form UifM, ar ilittlinf' ^*irrd)
HiB Shapn -
Fern tnm. AaehHrva,
art**"'
Contour Syatam ..
[Htky («r uM eantoan) .. .
I
LAND CLA6«FICAT10N
/Muthin M^iiTaH {or Fnsh Afarsft)-
StUt
Manhi
Wooded
\Cypro9o Swtunp
■Alt,' ,
»Hi iL
jju_ - l^f7l ^l
3b:
•u.
:3rr
lar-
" I nil/
:3sz
^uz
~S-F-^"^^*'gfc=g
..v. K- ••'
o^:f:i^i=^{^fe::^i^-^
>/-?:
WoOflto of Miiy kind (or m shown bohw)
Woods of Mny kind (or Bromd-LoMvd TrooB)
.Vj, '^j •'V 'V* ' * '•» --
Fig. 56
LAfa> CLA— tf^CATfOH
/¥m (or MuTow-LMvair 7>m^
;■•-
.*
T~r
AOoi
Aiya«tfto
ft
MAngrcm
Bamboo
4
♦ ^■»-
•^ ^-^V .
****..
♦v
Fig. 56
LAMCr CVASBiPACKTtOH^
CMCtUM
CK> _>-, -*rf -^^
-03.
4J ^ O S'^JS
« > ,^t>
a -^
%;r-^ . *^ ^^a'
^5> ,^
. ,' -" --
BMnATIM
OrchMrd
■j^ d $ <> .5
SV c^ C^ ^ ^
-^ 0 €» a ^
^> C-' fi^ ^ ^
GrMsaland i/i general
Tell Tropical Craas
^,\ /,-
>M.
Fig. 57
tANO CteAARHMCATMM
HYDROGRAffeMV. DANMCflS OBSTRUCTIONS
Shorelines
-{
Surveyed ....
Un9urvy9d
fTitUUFbdBtifuiykiad
(or M9 «Aewn bohw)
Shares and ,
Low- Wt^r Unes \
Rooky L§dg99
Sond
Mid
Grovel ond Rooko
Fig. 09
HYOROaHAFHY, PANOKft9« 0«STIIUCTIONti
ConJ P^fs.
K9ip
Eai GrM9s
RoGkuadw water
•♦• ♦
R90kawM$b (t tmy 8iMg9 pf Uf tUt^ ♦ *
M0ek whose pooitioD /• ^ouhtfid
♦ PD
Rook whose existenoe ie dtmbtfvd „ „ _ ♦ jr/)
Oyferfalls and Tkh Ripe
Umhing Danger Line
*■«••
WblrJpoole end MtUies ^_
Wreek ef eny kind (or Subwrgti DreJict)
Wreak or Dorset not submerged
#
Cebie (with or without httning).
Fig. 60
MYDROaRAWlY. OANGCI^S, OBSTRUCTIONS
Cumnt, not ikial, \mk€ity^ 2 knots
^
kn
fFlMi. ^kmoti
Tidal Curreats <
I knot
Fhod, %§komr.
\Bhb. 3d Aour „
I k»
■*-*■*■
or
III'
No bottom Mt 60 Fathoms ^ sb
Abbreviations relating to Bottoms
BC mud» S. SMnd, G. gnvl, Sb, 5A«//6» P. p9bhl*B, Sp. 4fMeto,
CI. clay, St. stoM8. Co. cor^. Oz, ooz; bk. bltok, wh. whit; nL r%d.
yl yUow, gy. gray, bu. bhi; dL dark. It. light, gn. gr—n, br. browa,
hrd, hard, aft. soft, fne. fin; ars. ooarae, Hey. rooky, sdh athky,
brk. broken, Irg. largo, sml amaU, atf. stiff, cat. oaJcareoua, doo.
docayod. rot. rottom, apk, apookH^, fly. fUnty, gty. gritty, grd. groumd.
atr. stroaky. vol. voloknh.
Fig. 61
1
HYDROGRAPHY. DAtUdCRK. ODfinrVVUCTIONS
i Fathom or 6 Foot Line
-- •.(»»*.*.*♦*— .**-^-*.-^-**-«f ..■■^•k-v.>^.>*^a^<.|i;h..«..«4..«...*,^*
2 Fathom or IS Foot Line
5 Fathom or 18 Foot Line
4 Fathom Line
4% Fathom Line
6 Fathom Line _ -.;
6 Fathom Line
10 Fathom Line
20 Fathom Line __
30 Faihom Line
40 Fathom Line _
50 Fathom Line ._
100 Fathom Line
too Fathom JL«ia «
ZOO Fathom Line.
600 Fathmn Line
1000 Fathom Line
2000 Fathom Line ,
SOOO Fathom Line
Pig. «2
AIDS TO NAVIOATION. ETC
f '
U/e-sMvittg SUitioD ^lss. (t)
UghtofMiiy kind {or UghthouM) j^
Lighthouse, on small somIo chsa-t •
Light Vossel of any kind ^
Light Vossols showing number ofmMMts ^ ^>A.
Light with Wireless ^ ^
L/fW Vessel with Wirekss @
Light with Submarine BeH
Light Vessel with Submariim Bell 4,
Light with Submarine Bell and Wireless - .. ^ ^
Light Vessel with Submarine B«tf and Wireless d)
Lighf^ , ^ •
Notiighfd ioA i 1 i I i 1
Sectors, shown by dotted lines
Abbreviations relating to Lights
F. fix*d. Pig. flMMhiDg, n. fiMsh, PU. /lA9h98, Sac sector. Rev. revo/v-
ing, B. •hotric, W. wHHo. R. rod, V. vui^d by, Qrp. group, O06.
ooouhiag, Int infrmittont, Alt MltornMting. m. miha, win. minutm;
$«c. 8«001ldt.
Fig. 68
Beacons
AIDS* TO NAVfQATlOW ETC.
(Buoy of Any kind (or R9d Buoy)
BUck.
Buoys <;
striped horizonUUy
Striped vertically .. .
Checkered
Perch And Squere .
Perch Md Ben
I Bell (or uee tint four symbols with,
word'' bell")
\Ughted
• • • •
AM***
WhiaUing {or uee first four eymboh 5 1 1 ?
with word " whatUng ")
& A b &
• • • •
Spindle or Stdke Udd word "spindle" i
,jf 9pece SiUews)
AbbreviatJODS relating to Buoys
C. cen, N. nun, S. spar, H. S. horizontad etripes, B. bleck. R. red.
W. white. V. S. vertical atripee. G, green, Y, yeihw. Ch. checkered.;
Anchorage \
Of any kind (or for large vessels)
For small veasels
■I
Mooring Buoy
V*J
Range or Track Line
Fig.. 64
SPeCIAL MfLITARY SYMBOLS
RegimenUU Headquarters iSl
brigade Headquarters „ 4d*3c
Division Headquarters so^ac
Corps Headquarters _ 'W'
lafantry in line c^
Infantry in column * §
C3
C±J
C±3
Cavalry in line i^*
Cavalry in column ' S
Mounted Infantry
..r
Artillery , i|. •!« iji .|1 .•,•
Sentry 6
Vidette i
Picket, Cavalry and Infantry pfc *«
Support, Cavalry and Infantry dw c*3
Wagon Train
Af^utant General
Quartermaster
Commissary
Fig. 6S
4
SPECIAL MILITARy SYMBOLS
Medical Corps F"
OrdiiMnce O
Sign&I Corps .., .., ..^ - P
EnginHr ioips \. :^
Gi/*a4«ery ...... ,,... , .. , .^....^ - '^^71^
Mortar Battery
'9- ■■» - *■ • '-- -r- ■•■■■"•■
• O 0'
Fart \.' •. . ' ■ i ' ^
> True plAn to be shewn ifknewn \
Redoubt ) (.....„
AAA
Camp AAAA
Battle ,. . ,....., , , , .:.._...., ^
Trenok .., u.-^n^^^^^'miii
Whep dolor is iised- execute thefolloy^i ik rt^
• . * -■ ' . \ i ^
AUUiS K^H^H^Hf'
Wife BntMnghAem
Palisades .' . i
« «» •
r* ^ ^ • 000
Contact mines .^ , o o o
ControHedmines ^o^^^^V^j
DemoliUons\ W^ifM
Fig. 66 a
LETTKRIHG
CIVIL DIVISIONS
Staters, Courvtij&s. Tbrwriahips. Capitals caul
Fnihoipal Ciiie^ fcJl oapiial letieitsf
ABCDEFGHIJ
KLMNOPQRST
UVWXYZ
Ibwns and VUlxjuge^s (wv^ Ctxp initi^aZm}
ab c def jghrjldmnopqrstuvwxy z
HYDROGRAPHY
Lexlee^s, Itb^er^ cuvd Bays (all capital ledkerm/
ABCDEFGHIJ
KLMNOPQRST
UVWXYZ
Creehs. Brooks, Springs, small Lakes, BotvoLs,
Marsh&s and. Glaciers fwUh. Cap.irvttiai9j
al>cdefghyhlntnop<jirstu-ywa:yz
Fig. fi6
tiCTTERIMe
MoztTvtcuTvs, Flatemat, £ins0 of Obif^
euui Ccmyons fall oapital lettesrs )
ABCDEFGHIJKLMNOPQRSTU
VWXYZ
Perciks, smajl J&tl&ys^ Canyons, Jslands and Foints.
(with €hp. mxtuda)
abcdefgh ij4( (hi nopqrstik V wxy z
PUBLIC WORKS
Itcuilroajd&, IRcnivels, 3ri$lgefS, Ferries, VajgoTv-ToaxLs,
TrailB, Fords <uuL Jhcms (oapitnU <mJy)
C ONTOUR NTJMBE RS
t2S^Se7S90
MARGINAL LETTERING
AB CDEFGHI JKLMNOPQRSTU
VWXYZ
^ (wHsfv Ccip. tnitucda)
a bcdef^h ij kl m nopqrstu vwx^ 2
1234-567890
Fig. 6# a
UETTEWMG
Names of ntttur^Uuid /^nturns. vprii^al M$Bhng
Names of Mituraf wmter featurea, slantihg hdering
Thickness W leUer f 0/ heigtU
Slope of letter 3 parts of base to 8 of height
AUTHORI2B0 ABBREVUTtOt^S
A
Arroyo
'L.S.S
. Life Saving Station
abut.
Abutment
L.H.
Lighthouse
A.
Arch
Long.
Longitude
b
Brick
Mt
Mountain
B.S
Blacksmith Shop
Mts
Moyn^ns
bot.
Bottom
N.'
North
Br
Branch
n.f.
Not fordable
br
Bridge
p.
Pier
C.
Cape
pk.
Plank
cem.
Cemetery
P.O.
Rost Office
con
Concrete
Pt.
Point
cov.
Covered
<W>
Queen-post
Cr.
Creek
R.
River
cul.
Culvert
R.H.
Roundhouse
D.S.
Dru^ Store
R.R
Railroad
E.
£*it
3- .
Soutb
Est.
Estuary
s.
Steel
f.
Fordable
S.M.
School House
Ft.
Fort
S.M.
Saw Mill
G.S
General Store
Sta.
Station
gir.
Gird«r
St.
Stone
G.M
Grist Mill
str
Strea m
i.
Iron
T.G.
Toll Gate
1
Island
Tres.
Trestle
Jc.
Junction
tr
Truss
kp.
King-post
W.T.
Water Tank
*
L.
Lake
W. W
Waterworks
Lat.
Latitude
W.
West
Ldg.
Landing
w.
Wood
Fig. 67
1
£ECOVHAIS8AirOE. «T
93. It a blot dmm on tb« drawing take a piece or blotting paper,
tear a comer or edge to eipone a frcnh Burtace. and bold It Id the
blot without touching the drawing nntil the surpluH Ink ts absorbed.
Tben press a drj blotter flrmly on the spot and tef It .
before attempting to erase. A piece of i ,.
Instead of blottlne paper, but should be Bllgbtly n
paper, but shoald be Bllghtly molstPncd to haste
r a large plot several pieces may be required.
IdIc are otsteel or rubber. A steel eraser or pel
aer of grltt
e aide glaxed
^ Bide ODly.
ide and read-
features they
verbal desig-
telllKlble and
to the \Tiay
"''file adaptatitn ot couventlonaf Blsaa to the size and scale of the
map la accomplished in part by varying the boldness of tlie pen >r
brush Blrofces and In part by wider spacing of tbem The strokes
must nevpr be so small as to render the sljni llletdble and never
lare F than can be easily made nith a CQCdliim pen The object Is to
produce a result nhieh nhlle distinct as to couTentlonal meaning
shall not be so heavy in Boneral lone aa to catch the eve or what la
especially Important In military maps to obscure anv additions which
may be made Topot:raphlcal signs should be perfectly clear when
looked (or but not obtmslYe
Aa a rouEh (-a'^le It may be stated that the bIrds shown In the
plates are about right for continuous areas of 3 squire Inches or leaa
In maps of scales of 2 or 3 inches to the mile It the map areas are
larK r or the scale smaller the sleos sh<uld be Ujihtened some but
Dot much by making the strokes smaller and M Bjaelng them wider
Some eiamples of good maps show the m adow al|.ir fur example
with two or three elements to the square Inch For verv larte scale
maps and for Qeld sketches the strokes may be made heavier and the
spacing In them close Tbcs remarks apply only to cultural signfl,
and a few others the significance of which Is In lependent of ulie and
shape All natural or artificial t atures in which sise and form are
In any wav material should be drawn with a? mu h r gard to the
scale aa practicable This becomes more important as the scale la
It may therefore happen that the same feature will he dllTerently
shown on maps of diff rent scales This Is <v°tl Ittustrated In tba
case of streams Fit ire 9? shows four signs for streams On a
large scale niap say 1 1 000 a rlvn et o few feet wide would be
shown by the second sign while on a scale of 1 1 000 000 a Stream
1 mile wide would be shown by the first sign
94346''— 17 6
08 ENGINEEE FIELD KAOTAL.
On ciyil maps explanatory matter is usually confined to notes. On
military maps much use should be made of explanatory matter in the
body of the map relating to single featurea The design, material,
and dimensions of bridges may be indicated ; the height and width of
channels and dimensions of locks and canals may be given : the width,
depth, and character of streams may be indicated, and ouier data of
tactical value may be set forth. This method of expression will be
more freely used as the maps or sketches are of less permanency or
more historical in character. For maps designed for permanent us^
or for use at an indefinite future time, this method must be employed
with caution, in view of the fact that most of such data is of change-
able type and may become obsolete, when its presence on the map will
do more harm than good.
97. Titles, notes, etc. — Every finished drawing should have a
descriptive title, consisting of —
(1) The designation of the organization under whose auspices it la
made, as Engrlneer Department | Bureau of Insular Aflalrsf
"War Department; Division of the Plilllpplnesf 1st Divi-
sion, 2d Corps.
(2) Its kinds, as map, sketch, plot, plan, profile, section,
or elevation. If more than one kind of drawing appears on the
sheet, each should be mentioned in the title, as plan and section*
of batteryi Plan, section, and elevations of irnardlioase,
etc.
(3) Its subject, if it relates to a particular object, feature, or
purpose.
(4) Its locality. This and the preceding may be interchanged in
position.
(5) Its sources, as Compiled froni, etc.; Reduced from, etc.f
From a survey, etc.
(6) Its authorship. If the work has been done by one person,
acting under the instructions of another, both should be named, as
under the direction of Colonel John Doe, Oeneral Btaff, by Captain
"Wllllani Roe, Xat U. S» Infantry,
(7) Its date.
Its linear scale; its contour interval; its scale of slope
equivalents.
Titles should be adapted in size and boldness to the size and im-
portance of the sheet They should be divided into lines, following
mainlv the divisions just stated. The middle letter of each line
should fall on a line drawn vertically through the middle of the
space allotted to the title. Lines should be alternately long and
snort, and if the long lines are symmetrically disposed, the effect Is
better.
To prepare a title, write down the matter under the various heads,
with proper connecting words, and divide it up into lines. Then
block out the title, observing the division of lines decided upon, and
make such alterations as seem desirable. Finally, letter the title on
the map. The following is an example :
Division of the Philippines. | Sketch map | of a tract of land
northeast of*] Zamboanga, | Island of Mindanao, | showing the
proposed location of . a I cantonment of U. S. troops. | From a
reconnaissance by | Capt. A B , I- Chief Ehigr., Department
of Mindanao, | Jan. 15, 1904. | Scale. | Contour interval, 20 ft.
Notes. — Besides the title, such information as will help to a proper
understanding of the meaning and value of the map should be given
in the form of notes. These usually relate to methods used in the
survey, datum points, etc.
Figure 68 shows the title corresponding to the above example,
with notes.
Meridian. — The magnetic meridian should be shown, and the tme
meridian also if the declination is known. The true meridian ma/
be a line, of 3 inches or upward in length, with a star at its nortn
and the feather of an arrow at its south end. The magnetic
BEGOlVNAISSAirCS.
DIVISION OFTHE PHILIPPINES.
SKETCH MAP
OfATRACTorLAND North east of
ZAMBGANGO,
ISLANDofMINDANAO.
\S/) o i^ing the prop oi^of k>c ati'o n of a
CANTONMENToF U.S.TROOPS.
Fjrom a Reconnaissance Br
Captain A B
Chief En &rI)ep't. ofMindana o.
Jan. 15, 1904.
Scale:
m » jw M9 nt*.
imM^-r^ I 1 I 1 I 1 I \ I
ConTour Interyai 20'
a
/° , ^° . J° , iT" kT?
A/o7io- E'/eva/ions are o6ove mean /.t^at^
Q. Af, wharf /n Zarruboan^o.
Flff.68.
lOe ENGINEER FIELD HULSJSAL.
meridian may be an arrow crossing the former at the middle point
and making with it an angle eauivalent to the declination.
Border. — ^The drawing should be Inclosed In a rectangle, preferably
with its sides N. and S. and E. and W. The border consists of two
Earallel lines, the inner one medium fine, the outer one medium
eavy, with a space between them equal to the width of the outer.
For geographical maps a double border is used, with space between
sufficient to contain the numbers of meridians and parallels.
Lietteriner. — Names and figures relating to points on the map
should be made parallel to one side. Names and figures relating to
extended features or large areas are disposed along the feature or
across the area in straight or curved lines.
Ornamental lettering should be avoided. A plain unshaded letter
is best. All needful variety of effect and prominence may be ob-
tained by the size, spacing, weight, and inclination of such letters
and the larger initials for Important words.
A very good effect may be obtained by the exclusive use of capitals.
The small letters require one-half the space of capitals in the same
line. They are not so easy to make well as the capitals, but can be
made more rapidly and look better on the face of the map. A very
good general rule is to use Inclined letters for all names and words
on the face of the map which relate to water and upright letters for
those which do not.
98. ESnlarsremeiit and reduction. — The simplest method Is by
squares. Divide the original into squares of 2 Inches or less by lines
drawn parallel to the borders (fig. 69). Divide the paper on which
the copy is to be made into squares with sides corresponding to the
same distance on the scale of the copy that the side of a square on
the original Itself does to the scale of the original Cfig- 70). If a
plotting scale of the original be placed on the side of a square on
the original and the plotting scale of the copy on the side of a
square of the copy, the readings should be the same. The square on
the copy will be larger If the drawing Is to be enlarged and smaller
if it Is to be reduced. The ratio between the sides of the squares on
the original and the copy is the ratio of reduction or enlargement.
This ratio must not be confused with the ratio of area of the two
maps, which Is different and not important.
Select a square of the original and reproduce Its contents In the
corresponding square of the copy ; or take a feature of the original,
as a road or stream, and trace Its course through several squares.
Usually the position of a point In a square or on one of the s^des
can be estimated with sufficient accuracy. Important points may bo
located by measurement of distances from the nearest sides of the
squares, using the scale of the map and the scale of the copy, re-
spectively.
Instead of drawing the squares^on the original, they may be drawn
on tracing linen or paper laid over It, or fine threads may be stretched
to form the squares. Every drawing board should have a scale of
inches on each edge marked with fine saw cuts or with small tacks
to facilitate the drawing of squares.
99. To measure an Irresnlar area. — Lay over the area a
piece of cross-section tracing paper (fig. 71). Count the full squares
inside the area and to their number add the sum of the estimated
fractional ones. In the figure the fractional squares to be added are
shaded. Multiply the equivalent number of full squares In the area
by the area of 1 square to the scale of the figure. If the scale
is 500 feet to the Inch=250,000 square feet to the square Inch, and
the squares ^ of an Inch on one side, then the area of one square Is
fhi of a square Inch, and Its value to the scale of 500 feet to 1
inch=2,500 square Inches=e 17.36 square feet. The number of squares
counted, multiplied by 17.36, is the number of square feet In the area.
If the scale Is distorted, the area per square inch of the drawing
is found by multiplying the scales together. Thus, in a profile plotted
to a horizontal scale of 500 feet to 1 inch and a yertical scale of 10
KBOOiraUSSAnCB.
102 ENGINEEE FISLB JCANTIAL.
feet to 1 inch, the area of a square Inch of the drawing; is 500 X lOas.
5,000 square inches. On such a profile a square of iV inch on a side,
or tIv inch area, corresponds to 50 square inches.
100. Verniers. — A vernier is an auxiliary scale ¥7 means of whicli
the principal scale can be read more closely than can be shown by
actual subdivision.
Consider AB (fig. 72) as part of a scale of equal parts. Constmct
the auxiliary scale or remier CD. the total length of which is equal
to 9 of the smallest divisions of the principal scale, but divided into
10 equal parts instead of 9, which makes each division of the vernier
A the length of the division of the scale.
When the zero division of the vernier, indicated by an arrow, is
coincident with a division, as 31, of the scale, the reading is 81, and
it is obvious that the first division of the vernier is to the left of 82
in the scale by ^ of the distance between 81 and 32. Similarly, the
second, third, etc., division of the vernier is two, three, etc., tenths to
the left of the 33, 34, etc., division of the scale. To make any division
of the vernier, as second, third, fifth, or eighth, coincide with the
division of the scale next ahead of it, th6 vernier must be moved
to the right two, three, five, or eight tenths of the length of one divi-
sion of the scale, and the arrow will then he opposite a point on
the scale two. three, five, or eight tenths of the distance from 81 to
32 ; or at 81.2, 31.3, 31.5, or 31.8. The quantity obtained by dividing
the value of one division of the scale by the number of divisions ox
the vernier is called the leaat count of tlie -vernier. But one
intermediate vernier division can coincide with a scale division at the
same time and the number of the coincident vernier division, counting
from the arrowhead, is the number of times the least count must be
added to the last scale division passed by the arrow to get the true
reading.
To read any vernier note the value of the 'last scale division passed
by the zero of the vernier and to it add the least count multipued by
the number of the coincident vernier division.
A vernier constructed as described is always read ahead of the
9iero, or in the direction in which the scale graduations increase, and
is called a dlreet -vernier. Verniers may also be constructed by
dividing the length of a certain number of divisions of the scale, aa
11, into equal parts one less in number, as 10. The principles of
operation and method of reading are the same, except that the coin-
cident line is to be found behind the zero of the vernier, or in the
direction in which scale graduations decrease. This form is called
retroflrr«<ie. It is but little used.
If the scale is graduated in both directions, as is often the case^
the vernier is doubled, the zero in the middle and each side forming
a direct vernier for the graduations increasing in the same direction.
This form is called double direct (fig. 73). The most compact
form is that shown in figure 74, called the folded -vernier, in wnlch
the graduations are numbered from the middle to one end and con-
tinue from the other end to the middle. This is read as a direct
vernier in either direction. If the coincident line is ahead of the
middle or In the direction of increasing graduation, take its number
from the middle as zero. If it is hehina the middle or in the direction
of decreasing graduation, take its number from the nearest end,
counting the end line as numbered on the vernier.
Verniers are also constructed on cylindrical surfaces (fig. 75) and
on conical surfaces (fig. 76). The principles and method of reading
are the same for all.
101. The engrineer'a transit. — This instrument la shown, and
the names of its parts indicated in figure 77. To use the transit,
set up the tripod, the legs extending far enough to give a stable
base and so as to make the top surface of the head norizontal or
nearly so. On level ground the legs will be equally extended. On
inclined ground the leg on the lower side will be stralghter and the
others more inclined. Remove the cap from the tripod and screw
on the instrument in its place. Hang the plumb line on the ho<A
&S00NNAIS8AHCE.
loa
T
T
^
a. 8 9
^
. 1
"V-
6 «
ti
ffv
Fig. 79
Fig. 73
Flg«7A
Fig. 75
Fig. 76
* V
'Q-E
,R-R-F
Y- S
EHSIHZEK PIBLD lUHnAL.
Addendum, 1307
EECONNAISSAHCE. 105
depending through the tripod head, and adjust Its length to brtng
the point of the plnmb bob as close as possible to the setting point.
Unclamp the vernier and turn the transit so that one of the plate
levels is parallel to one pair of leveling screws. The other plate level
will be parallel to the other pair. Bring the bubbles of the levels to
the center in succession by means of the leveling screws. Always
turn one of a pair down as the opposite one is turned up and avoid
more pressure of the screws against the plate than Is necessary for a
firm bearing. If a screw turns hard at any time it is either sprung or
has been set up too tight. In turning a pair of leveling screws
always move the thumbs toward each other or away from each other.
The bubble will follow the motion of the left thumb.
With the level bubbles in the centers of their tubes the plate will
be level if the bubbles are in adjustment. Turn the transit slowly
in azimuth and watch the bubbles. If they remain in the centers
the plate is level and the levels are also correct. If either bubble
leaves the center, the amount of its motion indicates the amount
by which it is out of adjustment. If the amount is small it may
be neglected ; if large, the adjustment should be made as hereafter de-
scribed. For short lines the level error may be neglected if the
entire bubble remains in sight during the entire revolution. Adjust
the leveling screws in this case so that the travel of the bubble will
bo equal on both Sides of the center.
Having leveled the plate, draw out the eyepiece until the cross
hairs are clearly defined. The instrument is now ready for use or
adjustment. Adjustments should be Invariably made in the order
in which they are described.
l«t adlnatanemt. — To make the axes of the plate levels perpen-
dicular to the axis of the instrument and therefore parallel to the
plate :
Having set op and leveled clamp the limb and revolve the plate
180**. If either bubble recedes from the middle of its tube bring
It back by raising the lower or depres^ng the higher end, one-half
by the main leveling screws and one-half by the small screws which
fasten the level to the plate. Again revolve the plate 180**, and if
the bubble still recedes from the middle correct the error as before
and repeat the operation until the bubble does remain in the middle
In both positions of the plate. When the adjustment is complete
both bubbles will remain in the center with the plate in any position.
2d adlnstnteiit. — To place the intersection of the cross wires in
the straight line through the optical center of the object glass and
perpendicular to the horizontal axis of the telescope.
The first adjustment completed, direct the telescope to some small,
well-defined, and distant object. With the screw which moves the
object-glass slide adjust the latter so that the distant object is as
distinct as possible. Both cross wires and object should now be
clearly seen. Note whether the image appears to move with reference
to the wires when the tye is moved from side to side across the
opening of the eyepiece. Such displacement is called parallax, and
indicates that the image is not exactly in the plane of the cross wires.
Move the object glass by its thumbscrew until the parallax ceases.
This must be dome every time tbe transit is ased to read an
angle, as well as when adjusting it.
Unclamp the plate and lay the intersection of the wires upon the
middle of a pin 200 or 300 feet distant ; clamp the plate ; plunge the
telescope, that Is, revolve it about its horizontal axis, and have a
pin driven at the same distance from the transit so that its mid-
dle shall be seen exactly at the Intersection of the cross wires.
Revolve the plate 180", clamp and lay exactly upon the middle of
the first pin. Again plunge the telescope and look at the second pin.
If the Intersection again strikes the pin the adjustment is correct,
but if the pin appears to one side of the intersection bring It back
one-quarter of the way by the side reticle screws, turning one in as
the other is turned out. If the instrument is erecting (most transits
are) loosen the reticle screw on the side toward which the wire should
106 ENGINEEB FIELD HANTTAL.
move in the field and tighten the other one. If inverUng^ turn the
other way. Repeat the process until the pins are cut exactly in the
middle without reference to position of transit or telescope. The
adjustment will then be correct.
8d adjustment. — To make the horizontal axis of the telescope per-
pendicular to the vertical axis of the instrument:
The instrument leveled, lay the telescope on a point at the top of a
nearly vertical line, such as the comer of a building ot a steady plumb
line. Clamp the plate and depress the telescope until the horizontal
wire is near the lower end of the vertical line and note the position of
the intersection of the wires with respect to the selected vertical,
whether to right or left of it, and how much. Revo
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