Mr. Hugh Miller, the geologist, when in the island of Eigg, in the
Hebrides, observed that a musical sound was produced when he walked
over the white dry sand of the beach. At each step the sand was driven
from his footprint, and the noise was simultaneous with the scattering
of the sand; the cause being either the accumulated vibrations of
the air when struck by the driven sand, or the accumulated sounds
occasioned by the mutual impact of the particles of sand against each
other. If a musket-ball passing through the air emits a whistling note,
each individual particle of sand must do the same, however faint be
the note which it yields; and the accumulation of these infinitesimal
vibrations must constitute an audible sound, varying with the number
and velocity of the moving particles. In like manner, if two plates of
silex or quartz, which are but crystals of sand, give out a musical
sound when mutually struck, the impact or collision of two minute
crystals or particles of sand must do the same, in however inferior a
degree; and the union of all these sounds, though singly imperceptible,
may constitute the musical notes of “the Mountain of the Bell” in
Arabia Petræa, or the lesser sounds of the trodden sea-beach of
Eigg.--_North-British Review_, No. 5.