Get two pasteboard tubes of the kind described for the pinhole telescope; the bore, or hole, of the first tube should be 1¾ inches in diameter and it should be 2 inches long. Have the second tube a little smaller than 1¾ inches in diameter on the outside so that it will slide easily into the larger tube and yet not leak light, and have this tube 1½ inches long. Paint the inside of both tubes with black paint to keep the walls of the tube from reflecting any stray rays of light which may strike them. The outside of both tubes can be covered with bookbinders’ cloth to give them a neat appearance. The next step is to mount the lenses. The larger lens for the object glass is a double convex lens 1½ inches in diameter and having a 4-inch focal length, or _focus_, as it is called for short. A lens of this kind can be bought for 25 or 30 cents. The smaller lens for the eyepiece is a double concave lens 1 inch in diameter and having a focus of 2 inches. This lens can be had for about 40 cents. [Illustration: FIG. 155.—OPERA GLASS TELESCOPE. CROSS SECTION.] Cut a strip of thin, tough cardboard ½ inch wide and 6 inches long; on this strip glue a strip of heavy pasteboard ½ inch wide and 5⅜ inches long, and have one end of both pieces even, as shown in Fig. 153. Set a flatiron on the pieces and let them dry. When dry make a groove down the middle of the heavy pasteboard by slicing out a very thin strip with the point of a sharp knife, being careful not to cut through the thin cardboard. Now bend the strips around the lens with the lens in the groove, glue over the thin end as shown in Fig. 154, and slip a a rubber band or tie a string around it to hold it in position until it has dried. The small concave lens, or eyepiece, is mounted in the same way, but since the lens is only 1 inch in diameter, cut the strip of cardboard ½ inch wide and 4¼ inches long and the strip of thick pasteboard ½ inch wide and 3½ inches long; this done glue them together, cut the groove and mount the lens as before. [Illustration: FIG. 156.—TELESCOPE. CROSS SECTION VIEW.] The next and last thing is to smear glue on the cardboard mounts and push the convex lens in the end of the large tube and the concave lens in the end of the small tube. Now slide the tubes together and you will have as good a telescope as the boy who invented it. It is shown in cross section in Fig. 155. You should, however, make two caps, one for each end of the telescope to cover the lenses when not in use. This little telescope is very handy to carry along on your scouting trips, as it takes up so little room, being only 2 inches long when closed up. =Telescope No. 2.=—This telescope is very much better than the one just described for seeing the stars as it magnifies about 4 times.