is attached to the primary axis. The cords can be easily slipped in the
holes by pulling their loops, but the friction is so great that they
cannot be slipped by pulling at either end. It takes about twice as long
to make the adjustment as would be necessary if a more expensive device
had been used; but this device is at once so cheap, so secure, and has
so seldom to be used, that it was thought to be best adapted for the
purpose. To prevent rotation from occurring about the primary axis when
it is not desired, a bar parallel to the secondary axis is attached by
its middle point to the primary axis near one end. A cord passes from
either end of this bar through cam shaped clamps, which were originally
designed for clamping the cords of curtains with spring fixtures. These
clamps are cheap. They are easily and quickly adjusted, and are very
secure.

The whole apparatus can be located upon the roof of a building, or, if
convenient, it can be mounted upon slides, and pushed through an open
window when it is to be exposed to the light. If it is to be used upon a
roof, a small hut, or shelter of some sort, near by is a great
convenience to the operator, particularly in winter.

_An Inexpensive Drying Case for Use in Coating the Paper._--When the
apparatus is in continuous use, time may be saved by having a convenient
arrangement for drying the sheets that have been coated with the
sensitizing liquid. I have made an inexpensive drying case which serves
the purpose very well. It consists simply of a light-tight rectangular
case of drawers. There are twenty-five drawers in all. They are
constructed in an inexpensive manner, and are the only parts of the case
that are worth describing. They are very shallow, being but 1-7/8 inches
deep, and as it appeared that the principal expense would be for the
materials of which the bottoms of the drawers should be composed, it was