ON THE EXISTENCE AND PROPERTIES OE THE ETHER. 



By D. L. Webster. 

 Presented by G. W. Pierce. Received September 12, 1912. 



Ix the science of mechanics of ordinary matter we are accustomed 

 to reo;ard velocity as essentially relative but acceleration as absolute; 

 and to say that, if a body is not acted upon in any way by other bodies, 

 its acceleration is zero, but that, if it is acted upon by any other body, 

 the accelerations of the two are opposite, and inversely proportional 

 to tiieir masses. But how can we test this law? and how can we 

 measure the acceleration? If we measure the velocity relative to the 

 earth, or to the sun, or to any star, at any two times separated by a 

 very short inter^'aI, how can we be sure that the system of reference 

 has not been accelerated during the time that has elapsed? And if 

 it has, on what svstem is its acceleration measured? 



This difficulty is made still more puzzling if we consider two mechan- 

 ical systems, such as the solar system, exactly similar in every way, 

 but one of which is removed to a practically infinite flistance from all 

 other matter while the other is subject to the attraction of a tre- 

 mendous mass, so large and far removed that its gravitational field 

 is practically uniform, and at absolute zero temperature so that no 

 rarliation would be received from it. These systems would be accel- 

 erated relativelv to each other, l:)ut which of them would be acceler- 

 ated? No obser\er on either of them could tell by any mechanical 

 means. 



An answer to these ciuestions appears to be given by the electro- 

 magnetic equations, which assume the especially simple form with 

 which we are familiar when expressed in terms of the length, mass, 

 and time units of any one of a certain set of systems, any one of which 

 appears to be mo\ing relative to any other with a constant velocity, 

 less than the velocity of light. These systems may all be assumed 

 to be unaccelerated, and assuming the impossibility of any system's 

 moving relative to one of these with a velocity greater than that of 

 light, we say that all other systems are accelerated. 



