To make a heliograph, get a board 12 inches long, 4 inches wide and 1 inch thick and cut a piece out of one end 4 inches long and 1 inch wide, as shown in Fig. 40. Bore a ¼inch hole through the slotted end and another ¼ inch hole 4½ inches from the slotted end, as shown in the cut. [Illustration: FIG. 40.—BASE FOR HELIOGRAPH.] [Illustration: FIG. 41.—BACK VIEW OF HELIOGRAPH.] Make a block of wood 4 inches long, 1 inch wide and 1 inch thick and bore a ¼ inch hole through it near one end. To the other end of this stick fasten a mirror about 4 inches square. This mirror should be perfectly smooth—a plate glass mirror is the best—and have a hole ¹/₁₆ inch in diameter drilled through the center of the mirror for sighting the heliograph, as shown in Fig. 41. Any optician will drill the hole for you for a quarter or less. Fig. 42 shows a top view of the heliograph and Fig. 43 shows a side view of it. Make a wood frame so that the mirror can be fastened in it and screw the frame to a stick of wood. Get a bolt 5 inches long and ¼ inch in diameter and have a thumb screw fitted to it. Set the end of the stick which has the mirror fastened to it into the slotted end of the baseboard, push the bolt through the holes and after slipping on the washer put on the thumb screw. The mirror can now be moved to and fro. [Illustration: FIG. 42.—TOP VIEW OF HELIOGRAPH.] [Illustration: FIG. 43.—SIDE VIEW OF HELIOGRAPH.] Into the hole in the front part of the base put a wire or a thin round stick to sight the mirror by. The heliograph is now ready for use. After sighting the mirror at the place where the signals are to be received, set the mirror so that the reflected beam of sunlight shines directly on the place. To send signals in the Morse code all you need to do to make dots and dashes is to place a sheet of cardboard before the mirror and take it away; the length of time the mirror remains uncovered determines whether it is a dot or a dash. The heliograph complete is shown in Fig. 44. [Illustration: FIG. 44.—HELIOGRAPH COMPLETE.] =How to Make a Simple Sundial.=—To make a sundial of the usual kind that will give the correct Sun time is not an easy matter, for the spaces marking the hours on the dial are not equal as they are on the face of the clock and this will make it hard to figure out. A kind of sundial that will give the correct Sun time though, can be easily made and at little cost. Get a strip of tin 2 inches wide and 24 inches long; mark it off into 24 equal spaces like those on a two-foot rule, and beginning at one end with the number 1, number each space to 24, as shown in Fig. 45. This done, bend the strip of tin into a perfect ring with the numbers inside and solder the joint, as shown in Fig. 46. [Illustration: FIG. 45.—NUMBERED STRIP FOR SUNDIAL.] [Illustration: FIG. 46.—TIN RING FOR SUNDIAL.]