from the margin of which projects at a right angle a long brass tube (Fig. 1), which carries the lens.  In Fig. 2 the lid of the box has been removed, and the bottom of the box, with the wheels, springs, and partially closed shutter, is presented.  The lid is double—­that is, it is a flat box in itself.  It contains nothing but the dry plate, supported at its center upon a small brass disk, against which disk it is firmly pressed by a pivot attached to a spring fastened in the lid.  The aperture in one side of this double lid, which corresponds with that seen in the floor of the box, may be closed by a slide, so that the lid containing the plate can be removed like an ordinary plate holder and carried to a dark room, where it is opened and the plate is changed.  When the lid is replaced this slide is removed, and as the shutter is made to revolve, the light falls upon whatever portion of the dry plate happens to be opposite the opening.

By reference to Fig. 2, it will be seen that when the large wheel which projects outside of the box is revolved by a crank, it turns the small ratchet wheel, which bears an eccentric pawl. (The crank has been removed in Fig. 2; it is seen in Fig. 1.) The central wheel has only six cogs.  The pawl is pressed into one of these cogs by a spring.  It pushes the central wheel around one-sixth of its circumference, when it returns to be pressed into the next cog.  While the pawl returns, it necessarily leaves the central wheel at rest, and whatever momentum this wheel carries is checked by a simple stop pressed by a spring upon the opposite side.  The central wheel carries a square axle, which projects through a small hole in the center of the double lid and fits into the brass disk before alluded to, causing the disk to revolve with the axle.  The disk is covered by rubber cloth; and as the dry plate is pressed firmly against the rubber surface by the spring in the lid, the plate adheres to the rubber and revolves with the disk.  Thus every complete revolution of the central wheel in the floor of the box carries with it the dry plate, stops it, and moves it on again six times.  The velocity of revolution of the plate is only limited by the rapidity with which one can turn the crank.

The shutter is revolved in the opposite direction by a wheel whose cogs are seen fitting into those of the little wheel carrying the eccentric pawl.

[Illustration:  FIG. 1.—­THE CAMERA MOUNTED.]

The two apertures in the shutter are so placed that at the instant of exposure of the plate it is momentarily at rest, while the plate when moving is covered by the shutters.  This arrangement prevents vibration of the plate and blurring of the image.  The camera is mounted by two lateral axles with screw clamps upon two iron stands, such as are in common use in chemical laboratories.  A brass rod attached to the tube steadies it, and allows it to be screwed fast at any angle corresponding to the angle at which