trough must be made for the size of the
film to be washed. Cut a 1/4-in. board as long as the film and a
trifle wider than the film's width. Attach strips to the edges of
the board to keep the water from spilling over the sides.

Cut a hole in one side of a baking powder can about half way
between the top and bottom, large enough to admit a fair-sized
stream of water from a faucet. Then solder the cover to the can
and punch a number of holes about 1/4 in. apart along the opposite
side from where the large hole was cut. Place this can on one end
of the trough, as shown, with the large hole up.

Some heavy wire bent in the shape of a U and fastened to the under
side of the trough at the can end will furnish supports to keep
that end of the trough the highest and place the opening in the
can close beneath the water faucet. A common pin stuck through one
end of the film and then in the trough close to the can will hold
it in position for washing. Five minutes' washing with this device
is sufficient to remove all traces of the hypo from the film.
--Contributed by M. M. Hunting, Dayton, O.

** Wood Burning [331]

[Illustration: Burnt Wood]

Burnt wood work done with an ordinary reading glass and the sun's
rays.

** The Diving Bottle [331]

This is a very interesting and easily performed experiment
illustrating the transmission of pressure by liquids. Take a
wide-mouthed bottle and fill almost full of water; then into this
bottle place, mouth downward, a small vial or bottle having just
enough air in the bottle to keep it barely afloat. Put a sheet of
rubber over the mouth of the large bottle, draw the edge down over
the neck and wrap securely with a piece of string thus forming a
tightly stretched diaphragm over the top. When a finger is pressed
on the rubber the small bottle will slowly descend until the
pressure is released when the

[Illustration: Pressure Experiments]

small bottle wilt ascend. The moving of the small bottle is caused
by the pressure transmitted through the water, thus causing the
volume of air in the small tube to decrease and the bottle to
descend and ascend when released as the air increases to the
original volume.

This experiment can be performed with a narrow-necked bottle,
provided the bottle is wide, but not very thick. Place the small
bottle in as before, taking care not to have too much air in the
bottom. If the cork is adjusted properly, the bottle may be held
in the ha