THE MYSTERY OP MATTER. 175 



which the action is conveyed. All these three things — matter, 

 the ether, and energy — have been thought to be, under present 

 conditions at least, uncreatable and indestructible. But whether 

 this is so or not is somewhat doubtful, for energy in the form 

 of light and heat radiated from the Sun and stars is con- 

 stantly being dissipated into space, and the phenomena of 

 radio-activity seem to render the absolute permanence of 

 matter more or less questionable. 



A certain number of physicists believe that there are only two 

 fundamental verities or entities ; some holding with Professor 

 J. J. Thomson that matter is really identical with electricity or 

 energy ; others like Lord Kelvin that the ultimate particles of 

 matter are of the nature of vortices or whirls in the Ether, and 

 are really separated portions of ether rotating with inconceivable 

 rapidity ; while others again consider the ether to be simply 

 a very highly rarefied and tenuous form of matter. But we shall 

 take it for granted that there are three distinct and fundamental 

 realities underlying all things — Matter, Energy, and the Ether. 



I have said that matter is especially characterized by what is 

 called inertia. This means that matter continues in its state of 

 rest or motion, whichever it may be, unless it be interfered with 

 by some force acting upon it from without. This applies 

 especially to matter in mass. Thus a body remains at rest until 

 it is caused to move by some external force, and when caused to 

 move would continue to move on at the same rate of speed for 

 ever, unless retarded and stopped by something outside itself. 

 Thus a bullet discharged from a rifle would go on travelling 

 at the same speed to all eternity, unless it were acted on by the 

 friction of the air and the attraction of the earth. 



We cannot create or destroy matter : we can transform it or 

 change its shape, but do what we will the amount of matter in 

 the universe remains exactly the same. Matter is impenetrable, 

 that is to say, no two portions of matter can occupy the same 

 place at the same time ; but it is also porous, that is, even in the 

 densest and most apparently continuous forms of matter, such 

 as the heavier metals, the idtimate particles of which it is 

 composed are separated from each other by fairly wide inter- 

 spaces, and these interspaces are occupied by ether. And in 

 some cases the spaces between the particles may be partly filled 

 up by particles of another kind of matter. The absorption of 

 gases by charcoal, and the absorption of hydrogen gas by the 

 metal palladium, are instances of this. And particles of one 

 kind of matter may pass through the spaces which separate the 



