ATOMS AND MOLECULES 53 



But they were right from their point of view, just as we are 

 right from ours, for with the knowledge that coal tar contains 

 the elements carbon, hydrogen, nitrogen and oxygen, which 

 are also contained in indigo, in quinine and in oil of bitter 

 almonds or in vanilla, we attempt to convert the coal tar into 

 one of these. The difference is that the alchemists failed while 

 we succeed, and our success is largely based upon the experi- 

 ence obtained from the unsuccessful efforts of our predecessors. 

 The other notion which originated in Greece was that of the 

 atoms, out of which all matter was supposed to be composed. 

 Democritus of Abdera is supposed to have invented the sug- 

 gestion that all matter is made up of little particles which 

 have their own separate existence and move about freely 

 until they happen to attach themselves to one another. 

 This idea occupied the attention of some other Greeks and 

 Romans, but during the Middle Ages it was entirely lost to 

 view; and in fact, its real importance was only recognized 

 after the already mentioned change had occurred in our views 

 concerning the elements. Now, under the lead of John Dai- 

 ton, we believe that the finest particles of which matter is 

 composed that we are able to recognize, are little bodies 

 which cannot be decomposed further by ordinary chemical 

 means, and which behave very much as if they were little 

 round pellets possessed of independent motion, and only in- 

 fluenced by those other little pellets that lie around them. 

 These atoms must have very many properties of their own, 

 and the different atoms do not necessarily have the same 

 properties. When two atoms, therefore, are alike in their 

 properties, we call them atoms of the same element; when the 

 properties differ, they are atoms of different elements. Now, 

 inasmuch as there are over seventy-five elements known to the 

 chemist, there must be at least seventy-five different species 

 of atoms. Whether these atoms are themselves made up of 



