oak were secured to the baseboard, just before each pin, as shown in Fig. 78.  This form gave great satisfaction.  A groove was cut in the side of one of the pins to receive the ring of a completed link, while the wire was passed through this ring and bent around the peg to form the ring of the new link.  After each link was formed it was carefully measured, and, if too long, was shortened by flattening the rings endwise, or, if too short, was lengthened by pinching together the sides of the rings.  There were fifty links in our chain, and every tenth one was formed with a double ring at the end, so as to distinguish it from the rest (see Fig. 79).

The Surveyor’s Rod.

We completed our outfit by making a surveyor’s rod out of a straight stick of wood about 6 feet long.  A target or sighting disk was mounted on the stick.  This disk was 6 inches in diameter, and was sawed out of a 6-inch square hoard by making straight cuts across the corners and then smoothing off the edge to a perfect circle with a draw-knife.  The thickness of the disk was only 1/2 inch.  At the back of the disk we fastened a block of wood with a slot cut in it to receive the rod, as shown in Fig. 81.  To hold the disk at different heights on the rod a small bolt was used.  The nut on this bolt was slipped into a hole on the block at the bottom of the slot and held in place by driving in nails about it, as illustrated in Fig. 82.  The bolt was then passed through the hole and threaded through the nut, with its inner end bearing against the rod.  The disk could thus be held at any desired position by tightening up the bolt.  A piece of white paper was now pasted over the disk.  The paper was marked off into quarters, and opposite quarters were painted black so that it would be easy to sight, from a distance, the exact center of the target.

[Illustration:  Fig. 80.  Cutting Out a Disk.]

[Illustration:  Fig. 81.  The Sighting Disk.]

[Illustration:  Fig. 82.  Nut Fastened in Block.]

A Simple Method of Surveying.

[Illustration:  Fig. 83.  Diagram of Our First Lesson in Surveying.]

Of course, none of us had studied trigonometry, but Uncle Ed devised a very simple method by which we could determine distances quite accurately without much figuring.

“If you will tell me the length of one side of a triangle and the angles it makes with the other two sides,” said Uncle Ed, “I’ll tell you the length of the other two sides and the size of the third angle.  This is how I will do it: 

“Say the line is 6 inches long and one angle is 35 degrees, while the other is 117 degrees.  Let us draw a 6-inch straight line.  This we will call our base line.  Now we will place the base edge of our protractor on the base line with its center at the right hand end of the line.  At the 37 degree mark we will make a dot on the paper so, and draw a line from the right hand end of the base line through this dot.  Now we will do the same thing