Provide a straight rod of glass or metal; strike it at the end in the
direction of its length, or rub it lengthwise with a moistened finger,
and it will yield a musical sound, which, unless its length be very
great, will be of an extremely acute pitch; much more so than in the
case of a column of air of the same length, as in a flute. The reason
of this is the greater velocity with which sound is propagated in
solids than in the air. If the rod be metal, the friction will be found
to succeed best when made with a bit of cloth, sprinkled with powdered
resin; or, if of glass, the cloth or the finger may be moistened and
touched with some very fine sand or pumice powder.
Generally speaking, a fiddle-bow, well resined, is the readiest and
most convenient means of setting solid bodies in vibration. To bring
out their gravest or fundamental tones, the bow must be pressed hard
and drawn slowly; but, for the higher harmonies, a short, swift stroke,
with light pressure, is most proper.