[Illustration:  Diagrams Showing Construction of Wonder graphs]

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