The electric connections are so simple that they are not shown in the drawings.  All that is necessary is a two-point switch, by which either L or M can be placed in circuit with the battery, and a press button in circuit with the bell and its cell.

If a gradual transformation is desired, a double-pointed rheostat could be used, so that as one light dims the other increases in brilliancy, by the insertion and removal of resistance coils.

With a clear glass and a dark room this model has proved to be fully as bewildering as its prototype.

** Experiment with Colored Electric Lamps [53]

To many the following experiment may be much more easily performed than explained:  Place the hand or other object in the light coming from two incandescent lamps, one red and

[Illustration:  Two-Colored Hand]

one white, placed about a foot apart, and allow the shadow to fall on a white screen such as a table-cloth.  Portions of the shadow will then appear to be a bright green.  A similar experiment consists in first turning on the red light for about a minute and then turning it off at the same time that the white one is turned on.  The entire screen will then appear to be a vivid green for about one second, after which it assumes its normal color.

** To Explode Powder with Electricity [53]

A 1-in. hole was bored in the center of a 2-in. square block.  Two finishing nails were driven in, as shown in the sketch.  These were connected to terminals of an induction coil.  After everything was ready the powder was poured in the hole and a board weighted with rocks placed over the block.  When the button is pressed

[Illustration:  Exploding Powder]

or the circuit closed in some other way the discharge occurs.  The distance 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]