FIG. 62 ONE-LEGGED TABLE AND LEVEL ] Repeat with other friends. Experiment 44. To make an engineer’s level. You can make one form of engineer’s level (Fig. 61) as follows: Take a full length of No. 6 tubing, bend it up 4 inches at each end, smooth the ends, attach it to a small board, rest the board on a one-legged table, and you have a serviceable level (Fig. 62). Fill the tube with water, shove the pointed end of the leg into the ground and sight along the outside of the upright tubes at the level of the water surfaces. The line along which you sight is exactly horizontal, because the water surfaces are at exactly the same level. Experiment 45. To use the engineer’s level. [Illustration: FIG. 63 HOMEMADE LEVEL IN USE ] An engineer’s level is used to find the difference in level of two or more points (Fig. 63). To practice using your level, find the difference in level of two points 100 feet apart on a road, sidewalk, or railroad. To do this, you must first make what is called a leveling rod. Find a piece of wood about one or two inches square and six or more feet long, mark on it feet and inches, beginning at the bottom end, and your leveling rod is complete. Now to find the difference in level of two points 100 feet apart, scratch a line or insert a small stake at one point, then pace off 100 feet and mark the second point. Now set up your level between the two points, ask a friend to hold the rod on the ground and upright, at the first point, sight along the water levels at the rod, and ask your friend to move his finger, or a white card, up and down until it is exactly in your line of sight. Now ask your friend to tell you exactly where his finger or card is and record this height. Let us suppose that it is 4 feet 6 inches above the ground. Now leave the level exactly where it is, ask your friend to hold the rod upright at the second point, and again sight along the water levels at the rod. Let us suppose that his finger or card is now exactly 3 feet above the ground. The difference in level at the two points is 4 feet 6 inches minus 3 feet or 1 foot 6 inches. That is, the second point is 1½ feet above the first point or the grade is 1.5 feet in 100, or 1.5 per cent. You can now mark a third point 100 feet beyond the second point, set up your level between the second point and third point, place the rod at the second point, then at the third point, and find their difference in level as above. If the third point is 1 foot above the second, the total rise in the 200 feet is 2½ feet; if, however, it is 1 foot below the second, the rise is 1½ minus 1 or ½ foot in the 200 feet. You can repeat this with as many points as you please. [Illustration: FIG. 64 A SPIRIT LEVEL ] Experiment 46. To make a spirit level. The spirit level (Fig. 64) is simply a curved glass tube filled with alcohol except for the bubble and closed at both ends. The curve of the tube is part of a circle. [Illustration: FIG. 65