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rection of the hind chainman, until it is in range with the
flag towards which the compass is sighted, and this process
is repeated at each chain measurement.

In railroad surveying, the line is divided into stations,
which are one hundred feet or one chain apart. At each
station a stake is driven and marked with a number corre-
sponding to the number of chains which the station is distant
from the starting point, which is numbered 0. When the
end of a course falls between regular stations, it is called a
sub-station, and the stake is marked by the number of the
immediately preceding station plus the number of feet from
it to the end of the course.

The line A B, in Fig. 255, is 650 feet in length. The
starting point A is numbered 0; each chain or one hundred

012 3 4 5 6 6+50

A FIG. 255. *

feet is marked by a stake with numbers in regular notation.

The point B, which is fifty feet from station 6, is marked

6 + 50.

1217. The Compass in Railroad Surveys. The

compass is of great value in running preliminary railroad
lines, where local attraction is absent or very slight. The
numerous delays encountered when running by backsights,



SURVEYING. 615

as in transit work, where all obstacles to the line of sight
must be cleared, are largely avoided in the use of the com-
pass. The directions of all lines are referred to the mag-
netic needle, and, in case of an obstruction, such as a tree or
a mass of rock, the compass can be quickly moved to the op-
posite side of the obstacle and the line continued without
delay. In case the line produced is a foot or two off the true
one, it is a parallel to it, and the error is not to be re-
garded as affecting the accuracy of preliminary information.
In the case of transit work, an error in the reading of an
angle is a cumulative one, and practically destroys the value
of the work. In the early days of railroad building, some
lines were surveyed and built with the aid of the compass
alone, but in America all location and construction depend
for their precision upon the transit.

1218. Organization of Party. A well-organized
compass party consists of a chief of party, compassman,
two chainmen, one flagman, two or more axmen, if the
country be thickly wooded, and one stakeman. If possible,
provide stakes of light, well-seasoned wood. For preliminary
lines where stakes do no permanent service, pine is best. A
convenient size is two feet six inches in length by two inches
in width and half an inch in thickness. A strong, active
stakeman will carry one hundred of these stakes, besides
the ax with which to drive them. Provide both chainmen
with marking crayons. The best crayon is of red chalk or
German kiel. They are bought in a crude state, but a little
work will shape them. They make a deep red mark, which
will stand exposure for years. Require chainmen to be
always provided with crayons. Instances of their forgetful-
ness too often occur. Require axmen to keep axes sharp.
A dull ax is little better than no ax. Check length of
chain with standard steel tape, lengthening or shortening by
means explained in Art. 1214. See that the compass is in
perfect adjustment. If the line to be surveyed is of consid-
erable length, a team of horses and driver with a strong
spring wagon should be a part of the outfit.



616 SURVEYING.

1219. Actual Work. The party is now prepared
to move. The compassman sets up the compass at .the
starting point, which is marked 0. The chief of party
goes ahead with the flagman, who carries a rod called
a flag. This rod is from eight to twelve feet in length,
and is divided into alternate red and white bands, each
one foot in length. The flagman sets this flag up at the
direction of the chief of party, the compassman sights
the instrument to it, and the chainmen commence meas-
uring the distance. The head chainman marks the stakes,
and should always keep at least ten stakes marked ahead
so as to avoid delay while measuring, and to insure con-
secutive numbering. Of these he need carry but five,
leaving the remaining five with the stakeman. He must
also carry a flag eight feet in length, and painted like
the one carried by the flagman; this flag is used for "rang-
ing in." As soon as the line is indicated by the head flag,
the axmen should fall to work clearing whate.ver obstacles
lie in the way of rapid chaining. By a little attention on
their own part and occasional direction from the chainmen,
they can keep well on line. At each station, and the
moment the hind chainman has put the head chainman in

line, the former should
carefully note the
number of the station
at which he stands and
call the number to the
chainman, who
must answer by repeat-

FIG. 256. -

ing the number next

in notation. Thus, if the hind chainman stands at Station
25 he must call " Station 25," and the head chainman must
reply "Station 26." The chainmen must be required to
hold the chain "taut" while measuring, and in as nearly
horizontal a position as possible. When the line of meas-
urement rises or falls abruptly, the chainmen must "break
the chain," as it is called. The best method of breaking the
chain is shown in Fig. 256.




SURVEYING. 617

Let A It be a. sloping surface lying in the line of measure-
ment. The point A is at Station 17. Stretchout the chain
to its full length and in proper line. The hind chainman
will be at Station 17. The head chainman here takes the
chain at the 50-foot tag and raises it until it is practically
level. The flag he carries for ranging in will serve for a
plumb line to mark the 50-foot point on the ground. The
hind chainman then calls the number of his station, 17, the
head chainman replying 17 + 50. The former then advances
to 17 + 50 and holds the middle tag at the point marked by
the rod. The head chainman then advances to the other
end of the chain and repeats the operation, reaching Station
18. When the slope is steep, the chain must be broken into
smaller sections. It is good practice for the flagman to
carry, besides his flag, a number of light stakes at least
eight feet in length and some strips of red flannel for
targets. If the view for the compass is open, as soon as
the compass is sighted and the flagman has a signal to that
effect, he should replace the flag by one of the stakes with
a piece of flannel attached and join the chief of party, who,
unless the line is to be produced, has gone ahead to select
another point for the flag. As soon as the compassman has
recorded the bearing of the line, he should take the compass
and walk rapidly to the next station, marked either by the
flag or target, and, if in full view of the chainmen, remove
the station mark and set up the compass and be prepared to
take the next bearing the moment it is indicated by the
chief of party. As soon as the chainmen reach the com-
pass and have "taken the plus" from the last full station,
the hind chainman calls out the full station and plus, which
the head chainman marks on a fresh stake and which the
compassman records as the length of the course run. If the
same line is to be continued or "produced," the compass is
set at the same bearing as the course just run and the
chainmen are lined in by the compassman.

122O. Example of the Use of the Compass in
Railroad Work. Suppose C A D in Fig. 257 to be a



618



SURVEYING.




4 7+75



railroad in operation, and that
it has been decided to run a
compass line from the point A
along the valley of the stream
X Y to the point B, The
bearing of the tangent A D
can not be determined by set-
ting up the compass at A, on
account of the attraction of
the rails. The direction of
this tangent, however, can be
obtained by setting up the
compass at A and sighting to
the flag held at D. The point
A, which is the starting point
of the line to be run, is
marked 0. Producing the line
A D 440 feet, the point E is
reached, which has been pre-
viously indicated by the chief
of party as a proper place for
changing the direction of the
line. The compass being set
up at E, the bearing of the
line A E, which is the line
A D produced, is found by
sighting to A, or, what is
preferable, to the point D,
if that point can be seen.
The number of Station /f,
viz., 4 + 40, and the bearing




SURVEYING. 619

of A E are then recorded by the compassman. By this
time the chief of party has located the point f, and the flag
is in place for sighting. The axmen, if there is work for
them to do, are put in line by the head chainman, clearing
only so much as would interfere with rapid chaining. The
bearing of the line E F being recorded, the compass is
moved quickly to /% replacing the target left by the flagman,
leveled up, and directed toward the point G, which is either
already, or soon will be, located. The chainmen reaching
F, its number 11 -f- 20 is recorded by the compassman, and
the instrument sighted to G and the work continued as
before.

1221. Form for Keeping Notes. A plain and con-
venient form for compass notes is the following, which is a
record of the survey platted in Fig. 257: The first column
contains the station numbers, the notation running from the
bottom to the top of the page. By such an arrangement,
the lengths of the courses are found by subtracting the num-
ber of the station of one compass point from the number
of the station of the next succeeding compass point.
Before commencing the plat, the subtractions are made
and the lengths of the courses written in red ink between
the station numbers.

The second column contains the bearings of the lines.
The bearing recorded opposite to a station is the bearing of
the course between the given station and the one next above.
Thus, the bearing recorded opposite Sta. is N 75 00' W,
and is the bearing of the line extending from Sta. to Sta.
4 + 40 next above. The length of the course is the differ-
ence between and 4 + 40 equal to 440 ft. The bearing
recorded opposite to 4 + 40 is N 25 00' W. It is the bear-
ing of the line extending from Sta. 4 + 40 to Sta. 11 + 20
next above. Its length is found by subtracting 4 + 40 from
11 + 20 equal to 680 ft., and so on.

In the third column, under the head of remarks, are
recorded notes of reference, topography, and any informa-
tion which may aid in platting or subsequent location.



620



SURVEYING.



Station.


Bearing.


Remarks.














47+75




End of line


35 + 75


N 25 40' E




27 + 50


N 14 10' E




20+35


N 2 30' W


Woodland


11 + 20


N 15 10' W




4 + 40


N 25 00' W







N 75 00' W


Sta. is at P. C. of 14 curve to






left at Bellford Sta. O. &P. R. R.



1 222. Platting. After a survey has been finished, a
drawing is made showing the courses. This drawing is
called a plat, and the operation of making the plat from
the field notes is called platting.

Since the direction of every line of a compass survey is
referred to the same parallel, viz., the magnetic meridian,
the readiest mode of platting such a survey is by the use of
the T square and protractor. The lines drawn to a T square
are parallel, and in platting take the direction of the mag-
netic needle, or meridian.

The line A B, described in Art. 122O and shown in Fig.
257, is platted as follows: The arrow shown in the figure
gives the direction of the magnetic meridian. A line A L,
parallel to this meridian, is. drawn through the starting
point A, and from A as a center the line A E, whose direc-
tion N 75 00' W is taken from the field notes kept by the
compassman, is laid off with a protractor. The directions
west are laid off to the left of the meridian, and those east
to the right of the meridian. The course A E, being a
northwest course, is laid off to the left of the meridian A L,
as shown in the figure. The length of the line A E is then



SURVEYING.



621



measured on this line to any convenient scale, usually 200
feet to the inch, and a parallel to the magnetic meridian
drawn through , from which the bearing of the line E F,
viz., N 25 00^ W, is laid off and platted. The remaining
courses are platted in the same manner.



TRANSIT SURVEYING.



THE INSTRUMENT.

1223. The engineer's transit, see Fig. 258, is an
instrument in which the telescope takes the place of the
plain sights of the compass,
and in which the angles are
read to single minutes by
the vernier. A level C is
attached to the underside
of the telescope and a ver-
tical arc D is attached to
the outside of the left hand
standard. A vernier E for
reading vertical angles is
attached to the telescope
axis and adjusted by the
tangent screw F. The
standards G and G, which
support the telescope, are
fastened to the upper or
vernier plate,' as is one of
the levels //, the other
being carried by one of the
standards at H' . The com-
pass circle K, which is
divided like that of the
ordinary compass, is also a
part of the upper plate. The vernier plate covers the lower
or divided limb, of which only two small arcs can be seen
through the openings where the verniers are placed. A




622 SURVEYING.

screw which clamps the vernier plate to the divided limb is
shown at k. Slow motion is given to the upper plate by
^ the tangent screw M, and to the divided limb by
the screw L. The transit is fastened to the plate
N by a ball and socket joint, and is leveled by
means of the screws P, Q, R, and .S. It is
fastened to the tripod T in a variety of ways,
usually screwed to the tripod, the edge of the
plate N being milled to aid the operator. The
transit is brought to center over a point by
means of a plumb bob which is suspended
by a loop fastened to the lower part of the
transit.

1224. The Telescope. The telescope is

a combination of lenses placed in a tube and so
arranged according to the laws of optics that the
image of any. object toward which the telescope
is directed shall be formed within the tube by
the rays of light coming from the object and
Is bent in passing through the object glass. This
o image is magnified by the eye-piece, which is
composed of several lenses. Telescopes are of
various kinds, some representing the object erect,
i. e., in its natural position, others representing
the object inverted.

The telescope shown in Fig. 259 represents the
object in an erect position. Rays of light from
the object A fall upon the object glass B where
they are bent, and, crossing each other, form the
image at C in an inverted position. Passing on
through the lens Z>, they are refracted or bent,
crossing each other again before reaching the lens
at E. Passing through the lens F they form an
erect image at G y which is in turn magnified by
the eye-piece H.

1225. The Cross-Hairs. In order that
the line of sight may be precisely brought to



SURVEYING. 623

bear upon any point of an object within the field of the
telescope, two fine lines called cross-hairs, or cross-
wires, are placed with their intersection at the common
focus of the object glass and the eye-piece. The inter-
section of these cross-hairs can be seen through the
eye-piece, and seems to be in the same position as that of
the image of the distant object.

The line passing through the intersection of the cross-
hairs and the optical center of the object glass is called the
line of collimation.

The cross-hairs are fastened to a thick brass ring placed
within the telescope and held in position by capstan

headed screws, Fig.
260, let into this ring.
They are commonly
placed at right angles to
each other, the one being
vertical and the other
horizontal. The ring,
together with the cross-
hairs, can be moved by
the capstan headed
screws. The cross-hairs

are either of platinum wire, drawn very fine, or spider threads.
Platinum wire is best, as it is not affected by changes of
temperature.

1226. Focusing the Telescope. The movement of
the object glass is effected by a milled headed screw U,
shown in Fig. 258. This screw moves the object glass out
or in, according as the object is nearer or further from the
instrument. The eye-piece is focused upon the cross-hairs
by a similar screw V. The cross-hairs are not in proper
focus until they appear to be a part of the object looked at,
showing no movement, however the position of the eye may
be changed.

The telescope is supported upon an axis and so placed that
both ends shall be as nearly balanced as possible. The axis




624 SURVEYING.

rests on upright legs called the standards. The standards
are fastened to the upper plate.

1 227. The Graduated Circle. This circle is divided
into 360 equal parts or degrees, and each degree is further
divided into two or three equal parts. If the degree is
divided into two equal parts, each part equals 30', and if
into three equal parts, each part equals 20'. The degrees
number from to 360, and in most instruments there is an
inner graduated circle, which numbers each way from to
90, as on the compass circle. Each tenth degree is num-
bered; each fifth degree is indicated by a longer line of
division, and each degree by a line longer than its
subdivisions.

1 228. Movements. When the line of sight is to be
brought to bear upon a distant object, the observer turns
the telescope in the direction of the object by lightly but
firmly grasping the upper plate, one hand on either side of
the instrument. The eye is ranged along the top of the
telescope, which is turned by the hands until it appears to
be in the direct line of the object. The eye is then brought
to the eye-piece, and the object glass focused upon the ob-
ject. The instrument is then clamped, and, by means of
either of the tangent screws, the cross-hairs are brought
to bear precisely upon any desired point of the object
viewed.

1229. The Levels. Most of the angles measured by
the transit are horizontal angles, but whether horizontal or
vertical, before an angle can be measured, the plate carry-
ing the graduated circle must be brought to a horizontal
position. This is effected by means of two small levels
placed on the plate at right angles to each other. Each
level consists of a glass tube curved upwards at its middle
and nearly filled with alcohol, leaving only space for a
bubble of air. They are so placed that when the air bubbles
are exactly in the middle of the tubes, the plate upon which
they rest will be in a level position. The leveling is



SURVEYING.



625



performed by means of four leveling screws. They have
milled heads and are arranged in pairs, the line passing
through one pair being at right angles to that passing
through the other pair.

1 23O. To Level the Instrument. Loosen the lower
clamp and bring one of the bubble tubes into a parallel to a
plane passing through a pair of opposite screws. By turn-
ing these screws, the air bubble can be brought exactly to
the center of the tube. As the tubes are at right angles to
each other, the putting of one in position for leveling ad-
justs the other for leveling also, and having leveled one tube
with one pair of screws, the other tube is leveled with the
other pair.

1231. The Vernier. A vernier is a contrivance for
measuring smaller portions of space than those into which




PIG. set.

a line is actually divided. The divided circle of the transit
is graduated to half degrees, or 30'. The graduations on the
verniers run in both directions from its zero mark, making
two distinct verniers, one for reading angles turned to the
right, and the other for reading those turned to the left.
Each vernier is divided into 30 equal spaces, which are to-
gether equivalent to 29 spaces on the divided circle ; hence,
each space on the vernier is equal to 29', and the vernier is
described as reading to minutes. In reading the vernier, the
observer should first note in which direction the graduations
of the divided circle run. In Fig. 261 the graduations in-
crease from left to right and extend from 57 to 91. Next
he should note the point where the zero mark of the vernier
comes on the divided circle. In Fig. 261, the zero mark
comes between 74 and 74. Now, as the circle graduations



026



SURVEYING.



read from left to right, we read the right-hand vernier
and find that the 23d graduation on the vernier coincides
with a graduation on the divided circle, and the vernier
reads 23', which we add to 74, making a reading of 74 23',
an angle to the left. In Fig. 262 the graduations on the
circle increase from right to left, and we accordingly read
the left-hand vernier. The zero mark of the vernier comes
between 67 and 68. Reading the vernier, we find that the




13th graduation on the vernier coincides with a graduation
on the circle, and the vernier reads 13'. Accordingly, we
add to 67, the vernier reading of 13', making a total read-
ing of 67 43', an angle to the right.



ADJUSTING THE TRANSIT.

1232. The constant use of an instrument tends to dis-
arrange some of its parts, which detracts from the accuracy
of its work, without in any way injuring the instrument
itself.

The correction of this disarrangement of parts is called
making the adjustments.

The transit, when leveled up, will, if in adjustment, fulfil
the following conditions, viz. :

1. It will maintain a perfectly horizontal position
during an entire revolution.

2. The line of sight, when directed in opposite direc-
tions, will be in the same straight line ; and

3. The line of sight will revolve in a vertical plane
perpendicular to the horizontal plane of revolution.



SURVEYING. 627

The adjustments should be made in the order of these
three conditions. The best time of the day for making the
adjustments, especially in the summer season, is the early
morning, before the air has become heated and the sun
dazzling.

1233. First Adjustment. Secure, if possible, an
open space where a clear sight may be had for at least 400
feet in both directions from the transit. Plant the feet of
the tripod firmly in the ground, and then bring the plate to
a horizontal position with the leveling screws. Next turn
the vernier plate half way around, i. e., revolve it through
an angle of 180. If the bubbles are in adjustment they
will remain stationary in the centers of the tubes. If they
do not remain so, but run to either end, bring them half way
back to the middle of the tubes by means of the capstan
headed screws attached to the tubes, and the rest of the way
back by the leveling screws. Then, revolve them again
through 180. Sometimes this adjustment is made by one
trial, but it is usually necessary to repeat the operation.

1 234. Second Adjustment. To cause the line of col-
limation to revolve in a plane :



400'



Measure from A, where the instrument is stationed (see
Fig. 263), 400 feet to the point B, where a pin (or tack, if
it can be seen) is fixed.

Carefully direct the line of sight to this point, and re-
verse the telescope, i. e., turn it on its axis until it points
in the opposite direction. If the line of collimation is "in
adjustment," a pin set 400 feet from A, on the opposite Side
of the instrument from B, will be at F and in the same line
as A B\ if it is not in adjustment, the pin will be on one
side of F, as at D. Turn the vernier plate half way around,
that is, through 180, and direct the line of sight again to B.



628 SURVEYING.

Reverse the telescope, and the pin will be at C. Carefully
measure the distance C D, and at E, one-fourth of the dis-
tance from C to D, set the pin. Move the cross-hairs by
means of the capstan headed screws until the vertical hair
shall exactly cover the pin at E, being careful to move them
in the opposite direction from that in which it would appear
they should move. This movement having been made and
the telescope reversed, the line of sight will not be at the
point B, but at G, a distance from B equal to C E. Again
sight to B, and, reversing, the pin will be at /", in the same
line as A B. It may be necessary to repeat the operation
to secure an exact adjustment. If so, take a new set of
points, a few inches removed from those first used, to avoid
confusion.

1235. Third Adjustment. To cause the line of
collimation to revolve in a vertical plane:

Suspend a plumb bob at as high an elevation as can be
A readily found; direct the line of sight to the
upper end of this line and then, revolving the
telescope slowly downwards, see if the intersec-
tion of the cross-hairs closely follows this line
throughout its length. If it does follow it, the
line of collimation revolves in a vertical plane.
If it does not, the adjustment may be made as
follows: Take a point A, in Fig. 264, on a church
spire or some other high object, and sight care-



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