ABSTRACT
The den of the photographer, in which he goes through those mysterious operations which are not submitted to the observation of the sitter, is a small room lighted by a window, and communicating into a dark closet, veiled with heavy curtains. The sense of the supernatural, always associated with dark closets, was excited strongly in the chamber, by the sound of a loud rumbling in the bowels of the house, and the visible departure of a portion of the wall to lower regions. The rays that have passed through to form the picture, have been called the photogenic rays: they refract not quite in the same way as the luminous or colorific rays, and therefore the focus of the photogenic picture and that of the picture thrown on the ground glass does not exactly coincide. For this, allowance has to be made in practice, and accurate instruments for ascertaining the true photogenic focus have been invented.
