ce between the nail points--which must be bright and
clean--should be just enough to give a good, fat spark.
--Contributed by Geo. W. Fry, San Jose, Cal.

** Simple Wireless System [54]

The illustrations will make plain a simple and inexpensive
apparatus for

[Illustration: Simple Wireless System]

wireless telegraphy by which I have had no difficulty in sending
messages across 1-1/2 miles of water surface. It is so simple that
the cuts scarcely need explanation. In Fig. 1 is seen the sending
apparatus, consisting of a 40-cell battery connected with two
copper plates 36 by 36 by 1/8 in. The plates are separated 6 in.
by a piece of hard rubber at each end.

In Fig. 2 are seen duplicates of these insulated plates, connected
with an ordinary telephone receiver. With this receiver I can hear
distinctly the electric signals made by closing and opening the
Morse key in Fig. 1, and I believe that in a short time I shall be
able to perfect this system so as to send wireless messages over
long distances.
--Contributed by Dudley H. Cohen, New York.

** Stop Crawling Water Colors [54]

To prevent water colors from crawling, add a few drops of ammonia
or lime water, or a solution of sal soda.

** Small Electrical Hydrogen Generator [54]

A small hydrogen generator may be made from a fruit jar, A (see
sketch), with two tubes, B and C, soldered in the top. The plates
E can be made of tin or galvanized iron, and should be separated
about 1/8 in. by small pieces of wood. One of these plates is
connected to metal top, and the wire from the other passes through
the tube B, which is filled with melted rosin or wax, to make it
airtight. This wire connects to one side of a battery of two
cells, the other wire being soldered to the metal top of the jar,
as shown. The jar is partly filled with a very dilute solution of
sulphuric acid, about 1 part of acid to 20 of water.

When the current of electricity passes between the plates E,
hydrogen gas is generated, which rises and passes through the
rubber hose D, into the receiver G. This is a wide-mouth bottle,
which is filled with water and inverted over a pan of water, F.

[Illustration: Hydrogen Generator]

The gas bubbling up displaces the water and fills the bottle.

If the receiver is removed when half full of gas, the remaining
space will be filled with air, which will mix with the gas and
form an explosive mixture. If a lighted match is then held near
the mo