106 THE POPULAR SCIENCE MONTHLY 



from any suspicion of being called a pragmatist. For him the ether un- 

 doubtedly is a real thing. In a more ambitious treatise published ten 

 } r ears ago, by Sir Joseph Larmor, entitled " Ether and Matter/' we 

 have a thoroughgoing mathematical investigation of the properties of 

 the ether, and, as the subtitle states, a development of the dynamical 

 relations of the ether to material systems. And yet, since the publica- 

 tion of the latter work there have been voices heard with ever-growing 

 distinctness, declaring in not dubious terms the lack of necessity of 

 any such conception as that of the ether, and threatening the belief in 

 its existence with relegation to the company of phlogiston in the morgue 

 of dead theories. That we can not dismiss such voices with contempt 

 is evident if among them are to be counted those of such leaders of 

 physical science as Henri Poincare, Sir J. J. Thomson and Professor 

 Max Planck. 



Before we can discuss the question of the existence of the ether, we 

 must first determine what we mean by that term. This is undoubtedly 

 the main difficulty with the whole matter. The article in the " En- 

 cyclopedia Britannica," written over thirty years ago by Maxwell, as 

 competent an authority as could have been named at that time, begins 

 with the definition, " a material substance of a more subtle kind than 

 visible bodies, supposed to exist in those parts of space which are ap- 

 parently empty," and ends with the statement, " Whatever difficulties 

 we may have in forming a consistent idea of the constitution of the 

 ether, there can be no doubt that the interplanetary and interstellar 

 spaces are not empty, but are occupied by a material substance or body, 

 which is certainly the largest, and probably the most uniform body of 

 which we have any knowledge." This is certainly flat-footed enough, 

 but how different from the conclusions of Lodge, one of the present 

 survivors of the same school, we may see from his book above mentioned. 



The need for the idea of an ether is well shown by the following 



quotation from Newton, who, after describing an experiment of two 



thermometers, one in a vessel filled with air and the other in vacuo, 



being carried from a cold place into a warm one, both rising at the same 



rate, says: 



Is not the heat of the warm Room conveyed through the Vacuum by the 

 Vibrations of a much subtiler Medium than Air, which after the Air was drawn 

 out remained in the Vacuum? And is not this Medium the same with that 

 Medium by which Light is transmitted, and by whose Vibrations Light com- 

 municates Heat to Bodies? 



And yet Newton did not accept the wave theory, but by the influ- 

 ence of his great name bolstered up the emission theory for a hundred 

 years. It was his contemporary Huygens, who must be credited with 

 the invention of the ether in order to explain the propagation of light. 

 Huygens's ideas of the properties of the ether were, however, very dif- 



