PHYSICS 325 



Taking energy first : All the numberless changes we see taking place 

 in the universe are, we think, manifestations of the interactions among 

 matter, ether and electricity. With every changing aspect of nature, 

 energy is passing from body to body and undergoing incessant trans- 

 formations, but its amount is always measurable by the work it may 

 accomplish when harnessed. 



Our knowledge of the uncreatable and indestructible character of 

 energy has given us a universal test which we may freely apply to all 

 phenomena to prove our knowledge of them. For when the required 

 energy relations are not satisfied by our explanations, it means we have 

 not got to the bottom of the case, but must strike deeper in to realize 

 the whole of the concealed mechanism. 



Charmed by the simplicity and sweep of the law of the conservation 

 of energy, a small school of physicists, who have mostly entered in by 

 the door of physical chemistry, have frankly set energy before inertia 

 and have endeavored to deduce matter and all else from it. This can 

 of course be done, for physics has become a body of thought so closely 

 knit together that all things in it are somehow related. Seen broadly, 

 however, the new method has few obvious advantages over the historic 

 procedure and not a few evident defects. 



Matter has two indisputable hallmarks, two properties in the pos- 

 session of which all the infinitely varied forms of matter unite, inertia 

 and weight. By inertia we mean that active resistance shown by every 

 piece of matter to any effort to change its motion; while the mutual 

 attraction between all material bodies, according to which all matter 

 strives to collect itself into one huge compact lump, we call gravitation. 

 The gravitational pull of the earth upon a portion of matter is its 

 weight. If we find anything in the world, however strange, which 

 possesses both inertia and weight, we may call it matter without further 

 examination. 



The ether which surrounds and encloses all our universe we came 

 first to know as the bearer of waves of light and heat. Ever since that 

 time we have known it to possess inertia; for no medium devoid of 

 inertia can carry forward a wave motion. 



Thus the ether has one of the hallmarks of matter. Has it also 

 weight ? This we can not hope to know until we find some way as yet 

 undiscovered to alter the natural distribution of ether between two por- 

 tions of space. Here it should be remembered that the weight of gases 

 was first proved after the invention of the air pump and barometer. 

 But, alas ! how shall we go about building an ether pump when all 

 material walls seem more porous to the ether than the coarsest sieve is 

 to air ? And worse, the ether appears to be incompressible. The ques- 

 tion of weight is thus at present in abeyance and we leave it. 



Of the properties of electricity alone, it is still difficult to speak. 

 The subject is easiest approached from the relations of electricity to 



