68 THE REALM OF ORGANISMS CONTRASTED 



atom is not the natural limit of the subdivision of matter, 

 that the stream of energy poured forth by radium is due to 

 a transmutation of the position of parts constituting the 

 atom, — the radium slowly changing into something else — 

 helium, and eventually lead. 



The individual molecules of matter in a gaseous state 

 are believed to move v^ith great velocity, incessantly collid- 

 ing with one another and rebounding, making impacts on 

 the walls of the vessel that contains them, or spreading 

 themselves through any space to which there is free access. 

 . . . AVe need not try to follow what is beyond our per- 

 sonal scope, but to illustrate the subtlety of modern con- 

 ceptions of matter — which is all that concerns us at pres- 

 ent — let us take a few sentences from Professor Soddy's 

 luminous Matter and Energy: — 



" Every cubic centimetre of any gas, measured under 

 standard conditions (0° C. and 760 millimetres baromet- 

 ric pressure), contains twenty-seven million million mil- 

 lion molecules. The weight of the single molecule of hydro- 

 gen is about three million-million-million-millionths of a 

 gram, and its velocity at 0° C. is rather more than a mile 

 a second. The hydrogen molecule is, it is true, the smallest 

 and simplest molecule of matter known, but it is a large and 

 sluggishly moving individual compared with another known 

 particle, the electron or atom of negative electricity " 

 (Matter and Energy, p. 82). 



When the temperature of a gas is lowered the molecules 

 come nearer one another, till their mutual tendency to draw 

 together restricts their wandering movements, and a liquid 

 is formed. Inside the surface skin of the liquid the molecules 

 move very rapidly, and collide so frequently that they fol- 

 low very zigzag paths, being perpetually turned back the 



