LUCRETIUS AND THE ATOMIC THEORY 183 



must be everlasting and indestructible. Lucretius, too, is so 

 persuaded of the great wear and tear that is going on, that he 

 remarks, if atoms had not been indestructible, everything would 

 have been destroyed by this time. The constancy of all pheno- 

 mena is a very good argument in favour of the indivisible atom, 

 for unless the component parts of a machine are unchanged, 

 how can the results produced be constant ? unless there be 

 really something indestructible and indivisible in sodium, how 

 can it happen that every little fragment shall retain every 

 physical property of sodium, so that, for instance, when glowing 

 with heat, it shall continually, as it were, ring out the same 

 notes of light, imparting such vibrations to our eye as paint the 

 well-known double yellow line ? If we could divide the little 

 bodies which, vibrating at those special speeds, prove sodium to 

 be glowing in the flame, they would no more vibrate at those 

 speeds than a cut violin-string would give out the true note to 

 which it had been tuned. By such division sodium would be 

 destroyed ; whatever might be the result, the body named 

 sodium would exist no longer ; but as yet no man has been able 

 thus to divide the sodium atom, and no one expects that bodies 

 will ever be decomposed into elements simpler than such as 

 would ring out a single note, a single line in the spectrum. In 

 other words, all men of science believe consciously or not in 

 atoms indivisible and imperishable. Lucretius certainly knew 

 nothing of spectrum analysis, nor of the law owing to which 

 chemical compounds have forced an atomic theory into daily 

 language ; but the arguments drawn from these sources are 

 simply special applications of his general theorem ; if matter 

 really obeys definite unchangeable laws, the ultimate materials 

 employed to make matter must themselves be definite and un- 

 changeable. Newton's exposition of this argument, quoted by 

 Mr. Munro to illustrate our author, is admirably clear : 



While the particles continue entire they may compose bodies of 

 one and the same nature and texture in all ages ; but should they 

 wear away or break in pieces, the nature of things depending on 

 them would be changed. Water and earth composed of old worn- 

 out particles would not be of the same nature and texture now with 

 water and earth composed of entire particles in the beginning. 

 And, therefore, that nature may be lasting, the changes of corporeal 



