THE ART OF SCIENTIFIC INVESTIGATION 





\''<:^^'j '-~'' 



EHRLICH S DRAWINGS OF HIS SIDE-CHAIN THEORY 



one can see from his illustrations of his side-chain theory. 

 Pictorial analogy can play an important part in scientific think- 

 ing. This is how the German chemist Kekule hit on the concep- 

 tion of the benzene ring, an idea that revolutionised organic 

 chemistry. He related how he was sitting writing his chemical 

 text-book : 



" But it did not go well; my spirit was with other things. I 

 turned the chair to the fireplace and sank into a half sleep. The 

 atoms flitted before my eyes. Long rows, variously, more closely, 

 united; all in movement wriggling and turning like snakes. And 

 see, what was that? One of the snakes seized its own tail and 

 the image whirled scornfully before my eyes. As though from a 

 flash of lightning I awoke; I occupied the rest of the night in 

 working out the consequences of the hypothesis. . . . Let us 

 learn to dream, gentlemen."^* 



However, physics has reached a stage where it is no longer 

 possible to visualise mechanical analogies representing certain 



56 



