er than employed. They have observed its action in weak
vessels, and are unduly impressed by its disasters. But they might
with equal justice point to exploded boilers as an argument against
the use of steam. With accurate experiment and observation to work
upon, Imagination becomes the architect of physical theory. Newton's
passage from a falling apple to a falling moon was an act of the
prepared imagination, without which the 'laws of Kepler' could never
have been traced to their foundations. Out of the facts of chemistry
the constructive imagination of Dalton formed the atomic theory. Davy
was richly endowed with the imaginative faculty, while with Faraday
its exercise was incessant, preceding, accompanying and guiding all
his experiments. His strength and fertility as a discoverer is to be
referred in great part to the stimulus of his imagination. Scientific
men fight shy of the word because of its ultra-scientific
connotations; but the fact is that without the exercise of this power,
our knowledge of nature would be a mere tabulation of co-existences
and sequences. We should still believe in the succession of day and
night, of summer and winter; but the conception of Force would vanish
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 afterwards 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 succession. But
a finer motion is at the same time set up and propagated. If the head
and ears be immersed in the water, as in an experiment of Franklin's,
the tick of the drop is heard. Now, this sonorous impulse is
propagated, not at the rate of a foot, but at the rate of 4,700 feet a
second. In this case it is not the gravity but the elasticity o