weak waves can produce effects which strong waves are incompetent to
produce? This is a feature characteristic of periodic motion. In the
experiment of singing into an open piano already referred to, it is the
accord subsisting between the vibrations of the voice and those of the
string that causes the latter to sound. Were this accord absent, the
intensity of the voice might be quintupled, without producing any
response. But when voice and string are identical in pitch, the
successive impulses add themselves together, and this addition renders
them, in the aggregate, powerful, though individually they may be weak.
It some such fashion the periodic strokes of the smaller ether waves
accumulate, till the atoms on which their timed impulses impinge are
jerked asunder, and what we call chemical decomposition ensues.

Savart was the first to show the influence of musical sounds upon liquid
jets, and I have now to describe an experiment belonging to this class,
which bears upon the present question. From a screw-tap in my little
Alpine kitchen I permitted, an hour ago, a vein of water to descend into
a trough, so arranging the flow that the jet was steady and continuous
from top to bottom. A slight diminution of the orifice caused the
continuous portion of the vein to shorten, the part further down
resolving itself into drops. In my experiment, however, the vein, before
it broke, was intersected by the bottom of the trough. Shouting near the
descending jet produced no sensible effect upon it. The higher notes of
the voice, however powerful, were also ineffectual. But when the voice
was lowered to about 130 vibrations a second, the feeblest utterance of
this note sufficed to shorten, by one half, the continuous portion of
the jet. The responsive drops ran along the vein, pattered against the
trough, and scattered a copious spray round their place of impact. When
the note ceased, the continuity and steadiness of the vein were
immediately restored. The formation of the drops was here periodic; and