The advance of photography : its history and modern applications (1911)

SOME EARLY APPLICATIONS OF PHOTOGRAPHY 217 thrown by the lenses on the ground-glass slide n o. The image is focussed either by shifting the objective by means of the screw at p, or by moving the lens at h, according as an enlarged image or one of life-size is desired. During the photographic process, an assistant must pull the ear muscle backwards and upwards, in order to give a proper direction to the funnel in the tortuous aperture of the ear. The exposure in the sunlight, if a good collodion was employed, lasted half a second ; under bright clouds on a clear day, from five to ten seconds, according to the intensity of the light. The exposure was effected by opening and closing a shutter at c d. In order to render photography more A accessible to physicians and scientific investigators, Dr Stein constructed an ingenious instrument called the " heliopictor," with which wet-plate photographs could be taken without any dark room. Fig. 99. The heliopictor was a kind of dark slide which could be placed at the back of any camera. Dubroni, of Paris, first constructed such developing boxes. This box, a section of which is given in the diagram fig. 99, contained a glass vessel K, into which a silver solution could be poured through a stopcock, not visible in the figure. The glass plate to be prepared was coated with collodion, then brought through the door T into the box, and placed on the aperture 0 of the vessel K. The door T w^as then closed, and the plate thus pressed by the spring a watertight against K. After this, the box was turned over to the right, the silver solution flowed over the plate and rendered it sensitive. The course of this operation could be observed through a yellow glass slide 8, which admits no light having any chemical action upon the sensitized plate. After the plate had been properly sensitized, the