44 SCIENCE AND IMMORTALITY 



or thousands, joined together in complexes known 

 as molecules. 



Now, what sort of thing are these atoms and 

 molecules ? How big are they ? The smallest 

 object that can be seen by the naked human 

 eye is 250 i^ch in diameter. A good microscope 

 reveals objects g^^^^^ inch in diameter ; and the 

 smallest object that, even theoretically, a perfect 

 microscope could show must measure at least 

 ^^Jqqq inch in diameter. Yet these magnitudes 

 are colossal compared with the size of an atom, 

 even compared with the size of the conglomera- 

 tions of atoms, known as molecules. 



The average diameter of the molecule of an 

 element was estimated by the late Lord Kelvin 

 and by Professor O. E. Meyer as about two-tenths 

 of a micro-micron, i.e. about 125,000.000 ^^ ^^ 

 inch. 



Professor J. J. Thomson has calculated that in 

 a cubic centimetre of gas at atmospheric pres- 

 sure {i.e. in as much gas as might be held 

 in a little box | inch square) there are about 

 20,000000,000000,000000 molecules ; and, of 

 course, in the same volume of a liquid or solid, 

 the molecules, being more closely packed, are 

 even more numerous. If closely packed, about 

 2,000000,000000,000000,000000 could be con- 

 tained in a little box an inch square. Even such 



