(B) With dark-ground illumination
Though not strictly bearing on photography, it is interesting to note that the X-rays, like the “gamma rays” (γ-rays) of radium, are in reality ether vibrations of very short wave length, and like the shorter waves (the ultra-violet) in sunlight, possess curative powers in some skin disorders and also the power of causing terrible burns. Sunburn does not result from exposure either to visible sunlight or to the heat of the sun, but to the ultra-violet rays; and an X-ray burn is identical with sunburn. In extreme cases the X-rays may cause complete destruction of the skin and even cancer, and before the properties of the X-rays were so well known as at present many operators lost hands, and some their lives, as a result of excessive exposure to the rays. At present, X-ray workers shield themselves, and, when necessary, the patient, with lead screens, that metal being practically opaque to the rays.
Color Photography
Many workers have tried, with varying success to devise a means whereby photography could be made to reproduce not only the outlines and gradations of natural objects but the colors as well, and there is now available a method of great worth for this purpose. In brief, it consists in making, by one exposure in an ordinary camera, a set of three-color negatives, each of which represents that portion of one of the primary colors—violet, green and red—which was reflected from the subject. That is, one negative represents the violet “sensation,” the second the green, and the third the red. Prints are made from these negatives in suitable dyes on transparent films, which are cemented together, one over the other, thus giving a true color photograph, in which the secondary and tertiary colors—blue, yellow, orange, purple, brown, etc.—are obtained, as in painting, by the mixture in proper proportions of two or more of the primaries. This is the first method of color photography to possess the great advantage of producing prints—not transparencies, so that any number of duplicates may be made. No special camera is required, and the process is within the reach of any careful amateur. The writer believes the artistic value of color photography is relatively slight—a black and white art is capable of the fullest intellectual expression, and color is merely sensuous in its appeal. After much experiment with different color processes, he finds his own monochrome (single tone) prints more satisfying than the color work. However, the value of color to the scientific worker is incalculable, as will be realized at once on considering only one of the possible applications—namely, the study of skin affections. It is interesting to note that several methods have been devised for the reproduction of natural colors in motion-picture work—the familiar method of coloring the positive film by hand being only an approximation to truth. But none of those presented up to this time is fully satisfactory, though the prospects of future development are good.
When we consider the manifold and widespread uses of photography and the pleasurable diversion that it affords, it seems safe to say that there is no other form of industry not an actual necessity that is of such importance to the welfare and happiness of the human race.
By courtesy of Dr. T. W. Harvey
RADIOGRAPH OF NORMAL HAND
SUPPLEMENTARY READING
| PICTORIAL PHOTOGRAPHY, PRINCIPLES AND PRACTICE | By Paul L. Anderson |
| INSTRUCTION IN PHOTOGRAPHY | By Sir William de W. Abney |
| SCIENCE AND PRACTICE OF PHOTOGRAPHY | By John R. Roebuck |
| PHOTOGRAPHY OF TODAY | By H. C. Jones |
| THE ARTISTIC SIDE OF PHOTOGRAPHY | By A. J. Anderson |