THE CONSTITUTION OF NATURE 9 



barn; there, under proper conditions, combustion might 

 be carried on; fuel might consume unseen, and metals be 

 fused in invisible fires. A body, moreover, once heated 

 there, would continue forever heated; a sun or planet 

 once molten, would continue forever molten. For, the 

 loss of heat being simply the abstraction of molecular 

 motion by the ether, where this medium is absent no 

 cooling could occur. A sentient being, on approaching 

 a heated body in this region, would be conscious of no 

 augmentation of temperature. The gradations of warmth 

 dependent on the laws of radiation would not exist, and 

 actual contact would first reveal the heat of an extra 

 ethereal sun. 



Imagine a paddle-wheel placed in water and caused to 

 rotate. From it, as a centre, waves would issue in all 

 directions, and a wader as he approached the place of dis- 

 turbance would be met by stronger and stronger waves. 

 This gradual augmentation of the impression made upon 

 the wader is exactly analogous to the augmentation of 

 light when we approach a luminous source. In the one 

 case, however, the coarse common nerves of the body suf- 

 fice; for the other we must have the finer optic nerve. 

 But suppose the water withdrawn; the action at a dis- 

 tance would then cease, and, as far as the sense of touch 

 is concerned, the wader would be first rendered conscious 

 of the motion of the wheel by the blow of the paddles. 

 The transference of motion from the paddles to the water 

 is mechanically similar to the transference of molecular 

 motion from the heated body to the. ether; and the prop- 

 agation of waves through the liquid is mechanically similar 

 to the propagation of light and radiant heat. 



As far as our knowledge of space extends, we are to 



