CONTEMPORARY ADVANCES IN PHYSICS 99 



ranges from somewhat over four to somewhat under nhie millions of 

 equivalent volts. The greatest amount of energy which men have yet 

 succeeded in loading upon a single charged particle or crowding into a 

 single quantum of radiation lies well below the first million of equivalent 

 volts; it still lay well below the first hundred thousand, ten years 

 after radium was discovered. The step from the tens of thousands to 

 the millions is a great one; this supplement voluntarily offered by 

 Nature, transcending immensely the greatest amounts of energy which 

 men can concentrate into a compact parcel, is chiefly responsible for 

 the advances in the understanding of energy and matter which radio- 

 activity made possible. 



The advances have indeed been great. Consider what ensued from 

 the discovery of the alpha-rays alone. With alpha-particles Ruther- 

 ford explored the interiors of atoms, and the results of his explorations 

 led him to the nuclear atom-model. The particles themselves he 

 proved to be atom-nuclei of a certain element, and they established the 

 amounts of electric charge which must be assigned to the atoms of that 

 element and all the others. The nuclear atom-model in turn supplied 

 Niels Bohr with the substructure of his theory; and Bohr's theory, 

 together with the phenomena which it inspired men to seek and find, 

 forms the half of contemporary physics. In the edifice of modern 

 physical theory, the alpha-particle is the cornerstone. Had Nature 

 not dispersed the radioactive substances through the rocks of the 

 earth, had there not been one or two of them long-lived enough to 

 survive and maintain a supply of their descendants until man arrived 

 and became scientific — or if the faint outward signs of the radioactivity 

 latent in the rocks had been overlooked, or having once been noticed 

 had been left unstudied — in any of these cases, centuries more might 

 have passed before a proper foundation was located for the edifice. 

 That is the prime reason for honoring those who detected radioactivity, 

 and then did not rest until they had brought it fully into the light. 

 Theirs is an illustrious history, and one not without pathos ; for some of 

 those who had worked with the greatest zeal found themselves in later 

 years the prey of a terrible and inexorable disease; like Prometheus in 

 the myth, they were consumed for having brought benefits to the human 

 race. Even yet the benefits which they gave have not been fully ex- 

 ploited ; marvelous things may still be discovered, in the process of 

 understanding the actions of the rays on living matter. But that will 

 be another story, and a long one. 



