524 PROCEEDINGS OF THE AMERICAN ACADEMY. 



To answer this question definitely seems impossible, but at any rate, 

 we can say that if it is granular and if these equations are to hold, the 

 structure must be exceedingly minute compared to the dimensions 

 of the electrons. A further suggestion is given by the fact that in the 

 geometrical equations, (1) and (2), the positive and negative quanti- 

 ties appear very similar, but seem to be more or less independent 

 of each other; while in the equation of motion (11), and in the phe- 

 nomena of vacuum tube discharges, etc., differences between the 

 actions of the positive and negative quantities appear, that seem to 

 show that not only are the electrons of the different signs made up 

 differently, but that the forces are transmitted by more or less inde- 

 pendent, and slightly different, structures in the medium. As this 

 condition of affairs seems to be incompatible with the idea of a con- 

 tinuous medium we are thereby led to the conception of a medium in 

 which there are probably two similar, but slightly different, interlac- 

 ing, granular structures, whose grains and distances between them are 

 inconceivably small, even compared to the electrons. 



The question of solid or fluid character of the ether appears easier 

 to answer; for if it were fluid, that is, if no amount of shear at any 

 point would change the properties at that point in such a way as to 

 affect the subsequent motions around it, a transverse wave would be 

 impossible. And if it were quasi-elastic, with effects analogous to 

 viscosity, that would enable it to transmit wireless telegraph waves 

 as well as the shortest known light waves, electrostatic forces around 

 stationary charges should be due to some effect entirely diflFerent 

 from that wdiich produces those of the wireless wave, so that slow 

 continued flow of ether might occur without hindrance. But the 

 changes of electric force near a moving electron may be much more 

 rapid than those of the wireless wave, and yet there appears to be no 

 viscous retardation of its motion. Furthermore, the aberration of 

 light and experiments such as that of H. A. Wilson ^ on the polariza- 

 tion of a dielectric cylinder rotating in a magnetic field seem to show 

 that no flow of ether occurs in moving matter. These considerations 

 and many others compel us to reject the fluid theory, and to say that 

 the structures of the ether are solid. But by "solid" we must not 

 mean possessed of ordinary solid elasticity, but merely that every 

 particle is permanently connected to the particles near it by con- 

 nections that cannot be deformed indefinitely, or even by a finite 

 amount without affecting the subsequent motion. 



7 H. A. Wilson. "Electric Effect of Rotating a Dielectric in a Magnetic 

 Field," Roy. Soc. Proc, 73, pp. 490-492. June 22, 1904. 



