Fig. 72. Sighting Blocks on the Baseboard. outer faces of the end blocks were now wet with mucilage and a hair was stretched vertically across the center of each sight hole. The hairs were then adjusted by sighting through the holes and moving the nearer hair sidewise until it was exactly in line with both the zero and the 180 degree marks on the cardboard. Then a hair was stretched horizontally across the center of each sight hole. Great care was taken to place the hairs at exactly the same height above the baseboard. To protect the hairs after they were adjusted, they were covered with a piece of glass, which was secured in place by tacks driven into the wood with their heads projecting over the edges of the glass.
Spirit Levels.
From one of his pockets Uncle Ed produced two small bottles, the kind used for holding homeopathic pills. These he filled nearly to the top with water, corked them and wedged them into grooves cut lengthwise in the baseboard at opposite sides of the cardboard ring. These grooves were filled with putty, and to make sure that the bottles were level with the baseboard the latter was floated on a bit of quiet water and the bottles were pressed down at one end or the other until the bubble within rested at the exact center.
The Tripod.
Fig. 73. The Tripod Head.
The tripod head was formed of a wooden disk 5 inches in diameter, with a wooden pin projecting from its center adapted to engage the hole in the circular piece above referred to. To the bottom of the tripod head were nailed three blocks
Fig. 74. The Tripod Leg. 2 inches long and 1 inch square in cross-section. The tripod legs were made of light strips of wood, 3/8 inch by 1 inch by 5 feet long, which we secured from one of the mills at Lumberville. Each leg was formed of two of these strips, nailed securely together to within 20 inches of the top. At the upper ends the strips were spread to receive the blocks on the tripod head. In this position they were held by headless wire nails driven into the ends of the blocks and fitting into holes drilled in the strips. For a plumb line we