Spiral illusions, 90 Spraying, paint, 187 Stereoscope, 39, 142 Stereoscopic vision, 38, 41, 141 Submarines, 225 camouflage for, 232 Sun, apparent enlargement at horizon, 169 Sunlight and skylight, relative proportions in nature, 215, 243 Terrestrial camouflage, 210 Theory of influence of angles, 98 perspective, 98 dynamic, 99 confusion, 100 indirect vision, 100 mean distance, 101 Thiéry's figure, 71 Thiéry's perspective theory, 99 Transparencies, 185 Twisted cord illusions, 88 Uibe, 167 Vertical vs. horizontal distances, 11, 36, 46 Visibility, low, for vessels, 222 of airplanes, 233 Vision, 29 persistence of, 131 stereoscopic, 38 Visual perception, 32, 33 Warm and cold colors, 158 Warner, E. L., 227 Wheatstone, 37 Wood grain, illusions caused by, 191 World War, 213 Wundt, 10, 11, 32, 74 illusion of direction, 79 Yellow spot, 139 Zöllner's illusion, 67, 76 Zoth, 175 OTHER BOOKS BY M. LUCKIESH COLOR AND ITS APPLICATIONS Second Edition, Revised and Enlarged. 6 x 9, 150 illustrations, 4 color plates, 431 pages. $4.50 The object of this treatise is not only to discuss the many applications of color, but to establish a sound scientific basis for these applications. The book is authoritative, well illustrated, and contains many references and a wealth of new material. It was written by an investigator in the general field of color and is therefore not narrowly limited in scope. It fills a distinct gap that has existed on the book shelves. LIGHT AND SHADE AND THEIR APPLICATIONS 6 x 9, 135 illustrations, 277 pages $3.00 The book is a condensed record of several years' research by the author in the science of light and shade. It is the first published work which deals with the science of light and shade in a complete and analytical manner. The author has the faculty of bringing forth scientific facts in such a manner as to be helpful to those interested in the various arts. The book is of extremely wide interest because it deals with the appearances of objects and hence with vision and with lighting. It is well illustrated and represents the first elaborate attempt to formulate the science of light and shade and to correlate it with various arts. ULTRAVIOLET RADIATION, Its Properties, Production, Measurement and Applications. 6 x 9, 12 plates, 270 pages $3.50