rates of vibration are the same as their own--and of the general series
of strings these only sound. The vibratory motion of the voice, imparted
first to the air, is here taken up by the strings. It may be regarded as
_absorbed_, each string constituting itself thereby a new center of
motion. Thus also, as regards the tightly locked atoms of molecules on
which waves of light or radiant heat impinge. Like the waves of sound
just adverted to, the waves of ether select those atoms whose periods of
vibration synchronize with their own periods of recurrence, and to such
atoms deliver up their motion. It is thus that light and radiant heat
are absorbed.

And here the statement, though elementary, must not be omitted, that the
colors of the prismatic spectrum, which are presented in an impure form
in the rainbow, are due to different rates of atomic vibration in their
source, the sun. From the extreme red to the extreme violet, between
which are embraced all colors visible to the human eye, the rapidity of
vibration steadily increases, the length of the waves of ether produced
by these vibrations diminishing in the same proportion. I say "visible
to the human eye," because there may be eyes capable of receiving visual
impression from waves which do not affect ours. There is a vast store of
rays, or more correctly waves, beyond the red, and also beyond the
violet, which are incompetent to excite our vision; so that could the
whole length of the spectrum, visible and invisible, be seen by the same
eye, its length would be vastly augmented.

I have spoken of molecules being wrecked by a moderate amount of heat of
the proper quality: let us examine this point for a moment. There is a
liquid called nitrite of amyl--frequently administered to patients
suffering from heart disease. The liquid is volatile, and its vapor is
usually inhaled by the patient. Let a quantity of this vapor be