Radiography
Some persons object to the inclusion of radiography as a branch of photography, since no camera or lens is used, but “photography” means, literally, “light-writing,” and radiography is precisely this.
If the air be nearly exhausted from a glass tube, so that a high vacuum exists therein, and it be then sealed up, a current of electricity may be sent through the remaining air, setting up ether vibrations that pass out from the tube. These ether waves have the power of passing through many substances that are opaque to visible light, the X-rays, as they are termed, being totally invisible, though light waves to which the eye is sensitive are set up at the same time within the tube. Many persons confuse the greenish light from an X-ray tube with the X-rays, but the two are actually entirely different manifestations. The X-rays, though invisible to the eye, are nevertheless able to affect a photographic plate strongly, so that photographs may be made through solid objects. For example, if a sensitive plate be laid on a table and the arm or the hand placed on it, and an X-ray tube is brought near the arm, a photograph results in which the bone is represented as a dark area and the flesh around it as lighter, this being, of course, simply a shadow picture. This affords an intensely valuable aid to diagnosis, and a good surgeon will, if possible, first radiograph a fractured bone before setting it, unless the circumstances are very exceptional. The value of radiography is not, however, confined to fractures, but extends to wounds (it is of great help in locating metallic fragments or other foreign bodies in a wound), to many intestinal disorders, and to the diagnosis of other diseased conditions.
STRIP OF MOTION-PICTURE FILM
Actual size. The photography consumed five-eighths of a second, or just long enough for the subject to turn her head
By courtesy of W. Faitoute Munn
MICROPHOTOGRAPH OF CRYSTALS OF BRUCINE SULPHATE
(A) By transmitted light