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and winter; but the soul of Force would be dislodged from
our universe; causal relations would disappear, and with
them that science which is now binding the parts of Nature
to an organic whole.

I should like to illustrate by a few simple instances the
use that scientific men have already made of this power of
imagination, and to indicate afterward some of the further
uses that they are likely to make of it. Let us begin with
the rudimentary experiences. Observe the falling of heavy
rain-drops into a tranquil pond. Each drop as it strikes the
water becomes a centre of disturbance, from which a series
of ring-ripples eXpand outwards. Gravity and inertia are
the agents by which this wave-motion is produced, and a
rough experiment will suffice to show that the rate of
propagation does not amount to a foot a second. A series
of slight mechanical shocks is experienced by a ‘ body
plunged in the water as the wavelets reach it in succes-
sion. But a finer motion is at the same time set up and
propagated. If the head and ears be immersed in the wa-
ter, as in an experiment of Franklin’s, the shock of the
drop is communicated to the auditory nerve—the tick of
the drop is heard. Now this sonorous impulse is propa-
gated, not at the rate of a foot a second, but at the rate of
forty-seven hundred feet a second. In this case it is not
the gravity, but the elasticity of the water that is the ur-
ging force. Every liquid particle pushed against its neigh-
bor delivers up its motion with extreme rapidity, and the
pulse is propagated as a thrill. The incompressibility of
water, as illustrated by the famous Florentine experiment,
is a measure of its elasticity, and to the possession of this
property in so high a degree the rapid transmission of a
sound-pulse through water is to be ascribed.

But water, as you.know, is not necessary to the conduc-
tion of sound; air is its most common vehicle. And you
know that when the air possesses the particular density

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