64 LIFE AND DEATH. 



able. — In physics we distinguish between two kinds 

 of matter — ponderable, obeying the law of universal 

 attraction or weight, and imponderable matter or 

 ether, which we assume to exist and to escape the 

 action of that force. Ether has no weight, or ex- 

 tremely little weight. It is material in so far as it 

 has mass. It is its mass which confers existence on 

 it from the mechanical point of view — a logical ex- 

 istence, inferred from the necessity of explaining the 

 propagation of heat, light, or electricity. 



It may be observed that the use of mass really 

 comes to bringing another element, force, to intervene, 

 and we shall see that force is connected with energy ; 

 thus it comes to defining matter indirectly by energy. 

 The two fundamental elements are not therefore 

 irreducible; on the contrary, they should be one and 

 the same thing. 



Energy is the only Objective Reality. — This fusion 

 into one will become more evident still when we 

 examine the different kinds of energy, each of which 

 exactly corresponds to one of the aspects of active 

 matter. Shall we define matter by extension, by the 

 portion of space it occupies, as certain philosophers 

 do? The physicist will answer that space is only 

 known to us by the expenditure of energy necessary 

 to penetrate it (the activity of our different senses). 

 And then what is weight? It is energy of position 

 (universal attraction). And so with the other attri- 

 butes. So that if matter were separated from the 

 energetic phenomena by means of which it is revealed 

 to us — weight or energy of position, impenetrability 

 or energy of volume, chemical properties or chemical 

 energies, mass or capacity for kinetic energy — the very 

 idea of matter would vanish. And that comes to 



