The bag changing box is the most satisfactory form of a magazine back to hold twelve quarter-plates in sheaths. This changing box consists of a box A with grooves at the front B to take a sliding shutter after the manner of a dark slide. The back C is removable to allow of the insertion of the block of sheaths D, and to it is fixed a spring E that forces the sheaths together. A bag F is fastened to GG; this bag is made of flexible material, and is of the shape shown. When the box is fixed in the slide rails of the camera, the shutter is drawn and the front plate is exposed. The plate is changed by gripping, with the thumb and forefinger, the top of the sheath II through the bag, withdrawing the sheath gently and pushing it in at the back. The next plate in the sheath is thus forced forward. A lever X is provided to lift the front plate.

Constructing Magazine Back for Camera.