L. Page — A Century's Progress in Physics. 347 



to have gotten abroad that in a few years all the great 

 physical constants will have been approximately esti- 

 mated, and that the only occupation which will then be 

 left to men of science will be to carry on these measure- 

 ments to another place of decimals." That he himself 

 did not entertain this view is made evident by a succeed- 

 ing paragraph. "But we have no right to think thus of 

 the unsearchable riches of creation, or of the untried fer- 

 tility of those fresh minds into which these riches will 

 continue to be poured. It may possibly be true that, in 

 some of those fields of discovery which lie open to such 

 rough observations as can be made without artificial 

 methods, the great explorers of former times have 

 appropriated most of what is valuable, and that the 

 gleanings which remain are sought after rather for their 

 abstruseness than for their intrinsic worth. But the his- 

 tory of science shows that even during that phase of her 

 progress in which she devotes herself to improving the 

 accuracy of the numerical measurement of quantities 

 with which she has long been familiar, she is preparing 

 the materials for the subjugation of new regions, which 

 would have remained unknown if she had been contented 

 with the rough methods of her early pioneers. ..." 



That Maxwell's forecast of the prospects of his science 

 was no overestimate will be granted by those who have 

 followed the progress of physics during the last twenty 

 years. Yet the work accomplished in the past appears 

 small compared to that which is left to the future. Many 

 of the unsolved problems are matters of fitting together 

 puzzling details, but there is at least one whose solution 

 appears to demand a radical modification in our funda- 

 mental physical conceptions. This is the formulation of 

 the laws which govern the motions of electrons and pos- 

 itively charged particles inside the atom. 



Black Radiation. — The significance of the problem was 

 first brought to light through the study of black radia- 

 tion. By a black body is meant one whose distinguishing 

 characteristic is that it emits and absorbs radiation of all 

 frequencies, and black radiation is that which will exist in 

 thermal equilibrium with such a body. The interest of 

 this type of radiation lies in the fact, demonstrated by 

 Kirchhoff, that its nature depends only upon the temper- 

 ature of the black body with which it is in equilibrium, 

 and on none of this body's physical or chemical charac- 

 teristics. Thus we may speak of the "temperature" of 



