of the rails. The direction of this tangent, however, can be obtained by setting up at A and sighting to a 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 previously decided upon 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 E, viz., 4+40, and the bearing of AE is 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 axemen, 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 F, replacing the target left by the flagman, leveled up and directed toward the point G, which is already located. The chainmen reaching F, its number 11 +20 is recorded by the compassman and the instrument sighted to G and the work continued as before.

Form for Keeping Notes.

A plain and convenient form for compass notes is the following, which is a record of the survey platted in Fig. 2: 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 number 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 at the course between the given station and the one next above. Thus, the bearing recorded opposite Sta. O is 75° 00′ W., and is the bearing of the line extending from Sta. 0 to Sta. 4+ 40 next above. The length of the course is the difference between 0 and 4+40 equal to 440 ft. The bearing recorded opposite to 4 + 40

is N. 25° 00′ W. It is the bearing 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 information which may aid in platting or subsequent location.

A vernier is a contrivance for measuring smaller portions of space than those into which 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. In reading the vernier,

3,0

20

110 •

110

20

60

710

810

FIG. 1.

30

the observer should first note in which direction the graduations of the divided circle run. In Fig. 1, the graduations increase 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. 1, the zero mark comes between 74° and

74%. Now, as the circle graduations 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. 2 the graduations on the circle increase from right to left, and we accordingly read the lefthand vernier. The zero mark of the vernier comes between 671⁄2° 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 672°, the reading = 13′ making a total reading of 67° 43′, an angle to the right.

Setting Up the Instrument.-In setting up a transit, three preliminary conditions should be met as nearly as possible, viz.: 1. The tripod feet should be firmly planted.

pletion of the operation is quickly performed with the leveling

screws.

How to Prolong a Straight Line.-Let A B, in Fig. 3, be a straight line which it is required to prolong or "produce”.

A

B

400'

FIG. 3.

ទ

The line can be prolonged in two ways-by means of foresight and backsight.

1. By foresight, set up the transit at A and sight to B; measure 400 feet from B in the opposite direction from A. Then, by means of signals, move the flag to the right or left until the vertical cross-hair shall exactly divide the flag held at C. Then, the line B C will be the prolongation of the line A B.

2.-By backsight, set the transit at B and sight to A. Reverse the telescope, and having measured 400 feet from B in the oppo

site direction from A, set the flag at C, then will the line B C be the line AB produced.

Horizontal Angles and Their Measurements. - A horizontal angle is one, the boundary lines of which lie in the same horizontal plane. Let A, B and C, in Fig. 4, be three points, and let

B

--143°30

FIG. 4.

it be required to find the horizontal angle formed by the lines AB and A C'joining these points. Set up the instrument precisely over the point A, and carefully

D 10+31

level it. Set the vernier at zero, and place flags at B and C. Sight to the flag at B and set the lower clamp. Then, by means of the lower tangent screw, cause the vertical cross-hair to exactly bisect the flag at B. Loosen the upper clamp. With a hand on either standard, turn the telescope in the same direction as that of the hands of a watch until the flag at C'is covered or nearly covered by the vertical cross-hair. Clamp the upper plate and with the upper tangent screw bring the line of sight exactly on the flag at C. The arc of the graduated circle traversed by the zero point of the vernier will be the measure of the angle BA C, as 143° 30'. The points A, B and Care not necessarily in the same horizontal plane, but the level plate of the instrument projects them into the horizontal plane in which it revolves.

A Deflected Line. -A deflected line or "angle line " is a consecutive series of lines and angles. The direction of each line is referred to the line immediately preceding it, the latter being, in imagination, produced and the angle measured between it and the next line actually run. The angles are recorded RT or LT, according as they are turned to the right or left of the prolongation of the

,1000 Ꮸ

98+90

AHB Benton Station

FIG. 5.

immediately preceding line. An example of a deflected line is

shown in Fig. 5. Starting from the head block of switch at Benton Station, O. & P. R. R.

Set up the transit at A with vernier at zero. Sight to a flag held at F on the center line of the track, O. & P. R. R. Loosen the vernier clamp, the point B being determined, and turn the telescope until the point B is distinctly seen; clamp the vernier, and accurately sight to flag held at B; the angle reads 32° 30′ and is recorded Rr 32° 30′, with a sketch showing the connection. The bearing of the line A B cannot be taken at A on account of the attraction of the rails. The point A is in the head block of switch (which is designated by the abbreviation H. B.) at Benton Station, O. & P. R. R. The instrument is now moved to B, the vernier set at zero and backsighted to A; the bearing of A B, viz., N. 75° 00' E., is taken, and the number of station B, viz., 2+90, together with the bearing of A B recorded. The telescope is then reversed, pointing in the direction B B'. The point C being determined, the upper clamp is loosened and the telescope turned to the right and sighted to C. The reading is found to be 14° 30′ and recorded RT 14° 30'. It measures the angle B' BC. The bearing N. 89° 20' E. is then recorded. The instrument is next set up at C, the vernier set at zero, backsighted to B, and then reversed; the deflection to D; viz., RT 10° 00′ read and recorded, together with the number of the station at C, viz., 6+ . 85. This deflection measures the angle C" CD and gives the direction of the line CD. A good form of notes for such a survey is the following.

Checking Angles by the Needle.-In spite of the greatest care, errors in the reading and recording of angles will occur. The best check to such errors is the magnetic needle.

In Fig. 6, we have an example of the use of the needle in checking angles. The bearing of the line A B, which corres