er band against the edge of a
thin triangular piece of wood which is attached to the face of the
fourth wheel. By substituting other plain figures for the
triangle, or outlining them with small finishing nails, many
curious modifications such as are shown by the two smallest
designs in the illustrations may be obtained. It is necessary, if
symmetrical designs are to be made, that the fourth wheel and the
guide wheel have the same diameter.

In Fig. 4, V and W are vertical wheels which may be successfully
connected with the double horizontal drive wheel if the pulley
between the two has a wide flange and is set at the proper angle.
A long strip of paper is given a uniform rectilinear motion as the
string attached to it is wound around the axle, V. The pen, P, has
a motion compounded of two simultaneous motions at right angles to
each other given by the two guide wheels. Designs such as shown as
a border at the top and bottom of the illustration are obtained in
this way. If the vertical wheels are disconnected and the paper
fastened in place the well known Lissajou's curves are obtained.
These curves may be traced by various methods, but this
arrangement is about the simplest of them all. The design in this
case will change as the ratio of the diameters of the two guide
wheels are changed.

These are only a few of the many adjustments that are possible.
Frequently some new device will give a figure which is apparently
like one obtained in some other way, yet, if you will watch the
way in which the two are commenced and developed into the complete
design you will find they are formed quite differently.

The average boy will take delight in making a wondergraph and in
inventing the many improvements that are sure to suggest
themselves to him. At all events it will not be time thrown away,
for, simple as the contrivance is, it will arouse latent energies
which may develop along more useful lines in maturer years.

** How to Make a 110-Volt Transformer [439]

Secure two magnets from a telephone bell, or a set of magnets
wound for 2,000 ohms. Mount them on a bar of brass or steel as
shown in Fig. 1. Get an empty cocoa can and clean it good to
remove all particles of cocoa and punch five holes in the cover,
as shown in Fig. 2. The middle hole is to be used to fasten the
cover to the brass bar with a bolt. The other four holes are for
the wire terminals. A piece of rubber tubing must be placed over
the wire terminals