nters. They may be sawed from pieces of thin board or,
better still, three of the plaques so generally used in burnt-.
wood work may be bought for about 15 cents. Use the largest one
for the revolving table T. G is the guide wheel and D the driver
with attached handle. Secure a piece of a 36-in. ruler, which can
be obtained from any furniture dealer, and nail a small block,
about 1 in. thick, to one end and drill a hole through both the
ruler and the block, and pivot them by means of a wooden peg to
the face of the guide wheel. A fountain pen, or pencil, is placed
at P and held securely by rubber bands in

[Illustration: An Easily Made Wondergraph]

a grooved block attached to the ruler. A strip of wood, MN, is
fastened to one end of the board. This strip is made just high
enough to keep the ruler parallel with the face of the table, and
a row of small nails are driven part way into its upper edge.
Anyone of these nails may be used to hold the other end of the
ruler in position, as shown in the sketch. If the wheels are not
true, a belt tightener, B, may be attached and held against the
belt by a spring or rubber band.

After the apparatus is adjusted so it will run smoothly, fasten a
piece of drawing paper to the table with a couple of thumb tacks,
adjust the pen so that it rests lightly on the paper and turn the
drive wheel. The results will be surprising and delightful. The
accompanying designs were made with a very crude combination of
pulleys and belts, such as described.

The machine should have a speed that will cause the pen to move
over the paper at the same rate as in ordinary writing. The ink
should flow freely from the pen as it passes over the paper. A
very fine pen may be necessary to prevent the lines from running
together.

The dimensions of the wondergraph may vary. The larger designs in
the illustration were made on a table, 8 in. in diameter, which
was driven by a guide wheel, 6 in. in diameter. The size of the
driver has no effect on the form or dimensions of the design, but
a change in almost any other part of the machine has a marked
effect on the results obtained. If the penholder is made so that
it may be fastened at various positions along the ruler, and the
guide wheel has holes drilled through it at different distances
from the center

[Illustration: Diagrams Showing Construction of Wonder graphs]

to hold the peg attaching the ruler, these two adjustments,
together with the one for