SCIENTIFIC USE OF THE IMAGINATION. 131 



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 di'op 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 t 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 



