We say that "seeing is believing," but it is not very hard to deceive the eye. The lines in Fig. 13 look absolutely parallel, and they are; but cross-hatch the spaces between them, with the hatching reversed in alternate spaces, as in Fig. 14, and they no longer look straight. Take the letters on the left, Fig. 15. They look all higgledy-piggledy, but they are really straight and parallel, as one can prove by laying a straight-edge against them, or by drawing a straight line through each letter, as shown at the right, Fig. 16. Such illusions were used on ships. Stripes were painted on the hull that tapered slightly, from bow to stern, so that the vessel appeared to be headed off at an angle, when it was really broadside to the watcher at the other end of the periscope. [Illustration: FIG. 13. Parallel lines that look straight] [Illustration: FIG. 14. Parallel lines that do not look straight] [Illustration: Courtesy of the Submarine Defense Association FIG. 15. Letters that look all higgledy-piggledy, but are really straight] There are color illusions, too, that were tried. If you draw a red chalk-mark and a blue one on a perfectly clean blackboard, the red line will seem to stand out and the blue one to sink into the black surface of the board, because your eye has to focus differently for the two colors, and a very dazzling effect can be had with alternating squares of blue and red. Other colors give even more dazzling effects, and some of them, when viewed at a distance, will blend into the very shade of gray that will make a boat invisible at six miles. When U-boat commanders took observations on a ship painted with a "dazzle" camouflage, they saw a shimmering image which it was hard for them to measure on the fine graduations of their periscopes. Some ships were painted with heavy blotches of black and white, and the enemy making a hasty observation would be apt to focus his attention on the dark masses and overlook the white parts. So he was likely to make a mistake in estimating the height of the smoke-stack or in measuring the apparent length of a vessel. A JOKE ON THE PHOTOGRAPHER Early in the submarine campaign one of our boats was given a coat of camouflage, and when the vessel sailed from its pier in the North River, New York, the owners sent a photographer two or three piers down the river to photograph the ship as she went by. He took the picture, but when the negative was developed, much to his astonishment he found that the boat was not all on the plate. In the finder of his camera, he had mistaken a heavy band of black paint for the stern of the ship, quite overlooking the real stern, which was painted a grayish white. The artist had fooled the photographer and at a distance of not more than two or three hundred yards! SEEING BEYOND THE HORIZON