Discontinuity in the Phenomena of Radiation 49 



For many years some of the best brains in Europe struggled to 

 show that there was, for instance, no essential difference between 

 the transmission of a beam of light through the ether, the trans- 

 mission of an earthciuake shock through the earth, and the 

 transmission of a wave through water. But it was just on the 

 nice combination in the ether of the property of rigidity possessed 

 by an elastic solid like the earth with the property of fluidity 

 possessed by watei', that full success was wanting. There came 

 a second phase Avhen Clarke Maxwell, abandoning attempts to 

 explain the physical properties of the ether in terms of those of 

 matter, essentially reversed the problem, and began the modern 

 attempt to found an electrical theory of matter by pointing out 

 the similarity of light waves to the electrical waves with which 

 we girdle the earth to-day — although Maxwell himself did not 

 live to see his prediction of the existence of these waves actually 

 verified. Tremendous success followed on this suggestion ; it 

 proved a landmark in the history of Physics ; but like all great 

 advances, it brought its own difficulties, and those difficulties have 

 accumulated until to-day it would appear that we are awaiting 

 the advent of another genius, a Newton or a Maxwell, to usher 

 us into a third phase. The trouble is, to put the matter in a 

 crude way, that the ether, so far from being a substance whose 

 existence is in doubt, has acquired such enormous importance 

 that we are hard put to it to explain why it does not possess all 

 the energy in the universe, and why matter, as we appreciate it 

 by our senses, possesses any at all and is not in reality the dead 

 and inert thing so scorned by a former generation of anti scientific 

 speculators. 



To appreciate the nature of the present impasse, I must ask 

 you to follow me into some considerations of a rather special 

 nature, concerned with the manner in which the physicist 

 measures radiant energy and in what particulars he distinguishes 

 one quality of radiation from another. To be sure, in the eye 

 one has an instr'ument in some slight degree suitable for that 

 purpose — but one too crude and too limited in its range to be of 



