This section is from the book "The Boy Mechanic Vol. 2 1000 Things for Boys to Do", by Popular Mechanics Co.. Also available from Amazon: The Boy Mechanic, Vol2: 1000 Things for Boys to Do.
By Bennett Blacklidge
A boy who likes to do the things that "grown ups" do can derive considerable pleasure from the making of a transit, which will enable him to start in surveying railroads, laying off town sites, and doing lots of kindred work. It is necessary to have a compass, and one, 1 3/4 in. in diameter, can be purchased at a reasonable price. A hole is bored with an expansive bit into a board, 7/8 in. in thickness, just deep enough to admit the compass snugly, then a circle, A, 4 1/2 in. in diameter, is drawn, having the same center as the compass hole, and the disk is cut out with a compass or scroll saw. A ring, B, is cut in the same manner from the same material, its inside diameter being such that the ring just fits around the disk A, and the outside diameter, 6 3/4 in. Another block, 5 1/2 in- in diameter, is glued to the bottom of the small disk A. This will appear as shown at C. A small hole is bored in the center of the bottom block on the under side to receive the threaded end of the screw on a camera tripod. By careful adjustment the threads in the wood will hold the transit firmly. A plumb bob must be attached exactly in the center of the tripod head. This can be easily done if the head is wood, but in case the top is of metal, the line can be attached to the screw with a double loop, as shown at D, so that the bob will hang centrally. Two standards are made as shown at E, each about 5 in. high, and fastened to the ring B in the positions shown in the drawing of the complete instrument. An arc of a circle is marked on one of the standards, as shown, to designate angles, the markings being laid out with a bevel protractor. The pointer is a hand from an old alarm clock.
Ill: Detail of Parts for the Construction of a Transit Which can be Used, with Fairly Accurate Results, in Doing Amateur Surveying for Railroad Work, Town Sites and the Laying Out of Maps
The telescope arrangement consists of a piece of pasteboard tubing, about 1 1/4 in. in diameter, one end being covered with a piece of black paper with a pinhole in the exact center, and the other equipped with "cross hairs." Four small notches are cut in the latter end of the tube, exactly quartering it, and two silk threads as fine as can be obtained, are stretched across in these notches. The tube is fastened to a block of wood, 5 in. wide and 7 in. long, with small tacks and two pieces of fine copper wire. This block is pinioned between the standards with two nails. The hand is secured to the nail in such a position that it will point straight down when the tube is level.
The instrument is adjusted in the following manner: It is set up where a lone tree can be seen, about one mile distant, and the center of the cross hairs is carefully set on the tree. Then a very fine wire is stretched across the compass, as shown at F, and while keeping it directly over the center of the compass it is also placed on a direct line pointing to the tree. Very small brass nails, driven in at G and H, serve to fasten it in the position thus found. When this adjustment has been made the telescope can be turned to sight any object, after first placing the instrument so that the needle points to the N on the dial, and a glance at the wire will show the exact direction in which the object is located.
The instrument is then taken to a level stretch of road and set up, and a stick is placed on end and marked at the height of the telescope. The stick is taken along the road about 200 yd., the telescope sighted on it, and the hand set. This makes the instrument level enough for all practical purposes. The plumb bob is then dropped, a distance of 20 ft. measured from it on the road, and a mark made. The telescope is sighted on this mark, and a mark is made on the standard at the point of the arc, to which the hand points. Another 20 ft. is measured, or 40 ft. from the bob, and another mark made. The telescope is sighted on it, and the location of the hand again marked. This works well up to about 300 ft., then the marks begin to come very close together. This method is used for laying out town sites. The instrument is set up directly over a stake from which to work, and the telescope is turned down until the 20-ft. mark is indicated, when the operator looks through the telescope and tells his helper where to set the stake. Then another is driven at the next point, and so on, until the limit of the instrument is reached.
When doing railroad surveying several start out together, one with an ax to cut away brush ; one to carry pegs: two to measure, or chain, the distance between stakes, and one to do the sighting. In this manner a line can be run that comes very near being perfectly straight for three miles.
A concrete example of how the transit was used to lay out a map of a ranch will now be given. The start was made on an east and west fence. The instrument was set 5 ft. from the fence at one point, and at the other end of the fence the stick was set at a point 5 ft. from the fence. When the stick was sighted, the wire cut the E and W on the compass, thus showing that the fence was set on a line, due east and west. The distance was measured from the fence to the house, which was 1/4 mile, and this was noted in a book. This operation was repeated on the rear, and the distance found to be 780 ft. while the compass showed the direction to be 4 deg. west of south. The next line ran 427 ft. and 1 deg. east of south. This was kept up all the way around. After these notes had been obtained, it was an easy matter to take a piece of plain paper and strike a line representing north and south and lay off the directions. A bevel protractor was used to find the degrees. The transit was set on the posts of the corrals and this saved the measuring out from the in-closure. The creek was surveyed in the same manner. So many feet southwest, so many feet west, so many feet 5 deg. south of west, and so on, until its length was run.
The transit can also be used for finding distances without measuring. A line from A to B is sighted, and F represents a point 1/2mile distant, the line from F to G being 100 ft. A line is now sighted from A, through G to C. A person standing at D is directed to move toward the point E and he is stopped as soon as sighted in the telescope. He then measures the distance from D to E. Suppose this distance is 250 ft. As each 100 ft. means 1/2mile, and the 50 ft., 1/4 mile, the point E is 1 1/4 miles from the transit. This method can be used quite extensively and distances obtained are fairly accurate.
CA small whisk broom makes a handy cleaner to brush the caked grease and lint from pulleys and gear wheels where waste and rags are useless.