can
be run by three dry cells. They need to give a fairly strong
light, especially L, which should have a conical tin reflector to
increase its brilliancy and prevent its being reflected in the
glass.

Since the stage should be some distance from the audience, to aid
the illusion, the angle of the glass and the inclination of the
doll, A, has been so designed that if the stage is placed on a
mantle or other high shelf, the image of A will appear upright to
an observer sitting in a chair some distance away, within the
limits of an ordinary room. If it is desired to place the box
lower down, other angles for the image and glass may be found
necessary, but the proper tilt can be found readily by experiment.

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
distan