THE PRESIDENTIAL ADDRESS 5 



Here let me make a confession which may also serve as an 

 apology. I have the unwelcome distinction of being the oldest 

 President the Association has ever suffered. In its primitive years 

 the average age of Presidents scarcely exceeded fifty : one of 

 them, aged only twenty-nine, afterwards founded the Cavendish 

 Laboratory, and so did a service to science which it would 

 be impossible to overvalue. As time went on the choice fell 

 on older men, and now the electors have taken what one hopes 

 may be regarded as an extreme step. But, as it happens, this is 

 not the first time I have read the President's Address. At the 

 Edinburgh meeting of 1921 the President, Sir Edward Thorpe, 

 was prostrated by illness and asked me to act as his mouthpiece. 

 The small service so rendered brought an unexpected reward. 

 Some newspaper report must have confused the platform substitute 

 with the real President, for a well-known novelist sent me a copy 

 of one of her romances which was no doubt meant as a tribute 

 to Sir Edward. It was called The Mighty Atom — an arresting 

 title. Perhaps that is why I did not read beyond the title-page. 

 Without close examination it was put by a more orderly hand than 

 mine on a shelf that already held works on like subjects by authors 

 such as J. J. Thomson and Rutherford and Bohr. The Mighty 

 Atom was said to be one of the best sellers of its day : in that 

 respect, if in no other, it found congenial company when it was 

 joined on the same shelf by a series of volumes from the fascinating 

 pens of Eddington and Jeans. These, however, I need not tell you 

 I have read and reread, to my entire pleasure and partial under- 

 standing. 



II. 



If * The Mighty Atom ' was an arresting phrase, it was also an apt 

 one. For we now know the atom to be indeed mighty in senses 

 that were little suspected by the begetters of atomic theory. It has 

 been mighty in sweeping away ideas that were found inadequate, 

 in demanding fresh concepts, in presenting a new world for con- 

 jecture and experiment and inference, in fusing chemistry and 

 physics into a single science. It is found to be mighty in the com- 

 plexity of its structure and the variety of radiations it may give 

 out when excited to activity. It has unravelled for us the be- 

 wildering tangle of spectroscopic lines. And, most surprising of all, 

 the atom, however seemingly inert, is mighty in being a magazine 

 of energy which, for the most part, it locks safely away. This is 

 fortunate, for if the secret were discovered of letting loose the 

 atomic store we should invite dissolution at the hands of any fool or 

 knave. And it is also fortunate that in the furnace of the sun, at 

 temperatures far higher than those of our hottest terrestrial infernos, 



