LUCRETIUS AND THE ATOMIC THEORY 195 



the potential energy of gravitation, elasticity, &c., may really 

 be due to the motion either of the atoms of gross matter, or of 

 their constituent parts. If matter in motion be conceived as 

 the sole ultimate form of energy, Leibnitz's proposition is 

 absolutely true, and Lucretius must be allowed great merit in 

 having taught that the motion of matter was as indestructible 

 as its material existence, although he knew neither the laws of 

 momentum nor of vis viva. If energy, as he believed, be due 

 solely to motion, then his doctrine is true. 



It is unnecessary further to state our author's theory in dis- 

 tinct propositions. He proceeds to explain the necessary pro- 

 perties of atoms. It is not odd, he says, that though they are 

 in continual motion, their sum (i.e. gross matter) seems to rest 

 in supreme repose. Atoms are too minute to be perceived ; their 

 forms, he says, are various, but the number of these forms is 

 finite. This doctrine corresponds to the modern idea of simple 

 or elementary chemical substances, each with its special atom, 

 but limited in number. There are, he thinks, an infinite 

 number of similar atoms. Infinite or not, the chemical theory 

 requires that there shall be a great many similar atoms, but 

 nothing, thought Lucretius, is formed of simple atoms; all 

 bodies, however minute, are compounds. Atoms have no colour, 

 nor are they hot or cold in themselves; they have neither 

 sound, scent, nor moisture as properties. All these properties 

 Lucretius believed to be dependent on the shape, motion, and 

 relative position of his atoms, but he makes only the most feeble 

 attempt to explain how these various properties can be thus 

 conferred, nor could this be done with the slightest hope of 

 success until the laws of these properties had been established 

 by long series of experiments. Something may now be done in 

 this direction, but it remains to be done, with one exception. 

 The motions producing the phenomenon of light are known, but 

 we do not know what moves. 



Of course, Lucretius believed organic bodies to be made of 

 atoms, and atoms only. Sentient beings, he thought, did not 

 require to be built up of sentient materials ; but we need not 

 discuss this conclusion, which follows of course from his assump- 

 tion that nothing but atoms and void exists, a mere assumption, 

 until the manner how atoms can build sentient beings be 



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