changing the other end of the ruler by
the rows of nails, will make a very great number of combinations
possible. Even a slight change will greatly modify a figure or
give an entirely new one. Designs may be changed by simply
twisting the belt, thus reversing the direction of the table.

If an arm be fastened to the ruler at right angles to it,
containing three or four grooves to hold the pen, still different
figures will be obtained. A novel effect is made by fastening two
pens to this arm at the same time, one filled with red ink and the
other with black ink. The designs will be quite dissimilar and may
be one traced over the other or one within the other according to
the relative position of the pens.

Again change the size of the guide wheel and note the effect. If
the diameter of the table is a multiple of that of the guide
wheel, a complete figure of few lobes will result as shown by the
one design in the lower right hand corner of the illustration.
With a very flexible belt tightener an elliptical guide wheel may
be used. The axis may be taken at one of the foci or at the
intersection of the axis of the ellipse.

The most complicated adjustment is to mount the table on the face
of another disc, table and disc revolving in opposite directions.
It will go through a long series of changes without completing any
figure and then will repeat itself. The diameters may be made to
vary from the fraction of an inch to as large a diameter as the
size of the table permits. The designs given here were originally
traced on drawing paper 6 in. square.

Remarkable and complex as are the curves produced in this manner,
yet they are but the results obtained by combining simultaneously
two simple motions as may be shown in the following manner: Hold
the table stationary and the pen will trace an oval. But if the
guide wheel is secured in a fixed position and the table is
revolved a circle will be the result.

So much for the machine shown in

[Illustration: Specimen Scrolls Made on the Wondergraph]

Fig. 1. The number of the modifications of this simple contrivance
is limited only by the ingenuity of the maker. Fig. 2 speaks for
itself. One end of the ruler is fastened in such a way as to have
a to-and-fro motion over the arc of a circle and the speed of the
table is geared down by the addition of another wheel with a small
pulley attached. This will give many new designs. In Fig. 3 the
end of the ruler is held by a rubb