Alum put into a tumbler of water, as it dissolves will assume the shape
of a pyramid. When the solution has nearly terminated, you will find the
mass covered with geometrical figures, cut out, as it were, in relief
upon the mass. This experiment having succeeded, take up a crystal
quartz which has six sides, and cut accurately from each face to a
perfectly convex surface, and place it on a piece of plate or common
window glass, a china or glazed plate, or any smooth surface, perfectly
clean, as grease or a particle of dust would impede its motion. Wet the
surface, and give the plane a slight inclination, when, if properly
managed, a rotatory motion will commence, which may be kept up for any
length of time by giving alternate inclinations to the plane surface,
according to the movements of the crystal; to heighten the pleasing
effect of which, a variety of paper figures, harlequins, waltzers, &c.,
may be attached. The first trial of the experiment had better be made by
giving a slight rotatory motion to the crystal.