While our naval vessels, that is to say war-ships, have adhered to the lead-gray war paint, the Navy Department has not declined to follow the lead of the merchant marine of this country and Great Britain in applying the art of camouflage to some of its transports, notably to the _Leviathan_, which, painted by an English camoufleur, Wilkinson, fairly revels in color designed to confuse the eyes of those who would attack her. A great deal has been written about land camouflage, but not so much about the same art as practised on ships. Originally, the purpose was the same--concealment and general low visibility--at least it was so far as the Americans were concerned. The British, on the other hand, employed camouflage with a view to distorting objects and fatiguing the eye, thus seriously affecting range-finding. The British system was known as the "dazzle system," and was opposed to the American idea of so painting a vessel as to cause it to merge into its background. The American camouflage is based on scientific principles which embody so much in the way of chromatic paradox as to warrant setting forth rather fully, even though at the present time, for good and sufficient reasons relating to German methods of locating vessels, the Americans have more or less abandoned their ideas of low visibility and taken up with the dazzle idea. A mural painter of New York, William Andrew Mackay, who had long experimented in the chemistry of color (he is now a member of the staff of navy camoufleurs), had applied a process of low visibility to naval vessels long before war broke out in Europe. The basis of his theory of camouflage was that red, green, and violet, in terms of light, make gray; they don't in pigment. The Mackay scheme of invisibility will be easily grasped by the reader if we take the example of the rainbow. The phenomenon of the rainbow, then, teaches us that what we know to be white light, or daylight, is composed of rays of various colors. If an object, say the hull of a vessel at sea, prevents these rays from coming to the eye, that hull, or other object, is of course clearly defined, the reason being that the iron mass shuts out the light-rays behind it. Mr. Mackay discovered that by applying to the sides of a ship paint representing the three light-rays shut out by the vessel's hull--red, green, and violet--the hull is less visible than a similar body painted In solid color. In a series of experiments made under the supervision of the Navy Department after we entered the war an oil-tanker ship was so successfully painted in imitation of the color-rays of light that, at three miles, the tanker seemed to melt into the horizon. The effect was noted in the morning, at noon, and in the evening. In the case of various big liners, more than 500 feet long, no accurate range could be made for shelling at from three to five miles--the usual shelling distance--while at eight miles the vessels melted into the ocean-mists.