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images of processes which, though mighty in the aggregate
beyond all conception, are so minute individually as to
elude all observation. It is the waves of air excited by
this tuning-fork which render its vibrations audible. It is
the waves of ether sent forth from those lamps overhead
which render them luminous to us ; but so minute are these
waves, that it would take from 30,000 to 60,000 of them
placed end to end to cover a single inch. Their number,
however, compensates for their minuteness. Trillions of
them have entered your eyes and hit the retina at the back
of the eye in the time consumed in the utterance of the
shortest sentence of this discourse. This is the steadfast
result of modern research; but we never could have reached
it without previous disoipline. We never could have
measured the waves of light, nor even imagined them to
exist, had we not previously exercised ourselves among the
waves of sound. Sound and light are now mutually help-
ful, the conceptions of each being expanded, strengthened,
and defined, by the conceptions of the other.

The ether which conveys the pulses of light and heat
not only fills the celestial spaces, bathing the sides of suns
and planets, but it also encircles the atoms of which these
suns and planets are composed. It is the motion of these
atoms, and not that of any sensible parts of bodies, that
the ether conveys ;' it is this motion that constitutes the
objective cause of what in our sensations are light and
heat. An atom, then, sending its pulses through the infi-
nite ether, resembles a tuning—fork sending its pulses
through the air. Let us look for a moment at this thrilling
ether, and briefly consider its relation to the bodies whose
vibrations it conveys. Different bodies, when heated to the
same temperature, possess very different powers of agitat-
ing the ether: some are good radiators, others are bad
radiators; which means that some are so constituted as to
communicate their motion freely to the ether, producing

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