io Instinct and Intelligence 



of conceivable mechanical subdivision, it can 

 be decomposed into its constituent elements- 

 hydrogen and oxygen. The word molecule is 

 thus employed to represent the smallest single 

 particle of any substance, whether elementary 

 or compound that has a separate existence; 

 whilst the word atom denotes a constituent ele- 

 mentary particle of a molecule. 1 Atoms are 

 now held to consist of a central nucleus around 

 which multitudes of electrons constantly re- 

 volve. 2 The structural arrangement and motion 

 of atom-clusters are all important as being the 

 directing agents of the kind of work performed 

 by various kinds of matter. For instance, the 

 molecules of the two substances known as 

 benzonitrile and phenylisocyanide each contain 

 seven atoms of carbon, five of hydrogen, and 

 one of nitrogen. There is a small difference in 

 the arrangement of the atoms of these two sub- 

 stances, and this slight difference in their atomic 



1 Matter and Energy, by Frederick Soddy, F.R.S., p. 48. 



2 " Electrons have been described as immaterial in the sense that 

 they arc not matter, but something at once finer grained and 

 endowed with fundamental qualities which distinguish them from 

 any known kind of matter ; they revolve thousands of millions of 

 millions of times per second, so that it might be supposed impos- 

 sible to measure the electron ; but as a matter of fact no magni- 

 tudes in science are known with greater exactitude." Matter and 

 Energy, pp. 170, 175, 187. 



