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 before inserting them in the holes.  Fill the can with crude oil, or with any kind of oil except kerosene

[Illustration:  Parts of the Transformer]

oil, and immerse the magnets in it by fitting the cover on tight (Fig. 3).  The connections are made as shown in the diagram, Fig. 5.  This device may be used on 110-volt current for electro-plating and small battery lamps, provided the magnets are wound with wire no larger than No. 40.  —­Contributed by C. M. Rubsan, Muskogee, Okla.

** Experiment with a Vacuum [439]

[Illustration:  Experimental Apparatus]