398 



SCIENCE. 



[N. S. Vol. IV. No. 90. 



and that tlie specific inductive capacity of 

 the medium consists of two parts, one due 

 to the ether, the other to the setting of the 

 molecules along the lines of electric force. 

 Starting from this supposition we can 

 easily see without mathematical analysis 

 that the relation between the refractive 

 index and the frequency must be of the 

 kind indicated by the curve. Let us sup- 

 pose that an electro-motive force of given 

 amplitude acts on this mixture of molecules 

 and ether, and start with the frequency of 

 the external electro-motive force less than 

 that of the free vibrations of the molecules ; 

 as the period of the force approaches that of 

 the molecules, the effect of the force in pull- 

 ing the molecules into line will increase, 

 thus the specific inductive capacity ; and 

 therefore, the refractive index, increases 

 with the frequency of the external force ; 

 the effect of the force on the orientation of 

 the molecules will be greatest when the 

 period of the force coincides with that of the 

 molecules. As long as the frequency of the 

 force is less than that of the molecules, the 

 external field tends to make the molecules 

 set so as to increase the specific inductive 

 capacity of the mixture ; as soon, however, 

 as the frequency of the force exceeds that 

 of the molecules, the molecules, if there are 

 no viscous forces, will all topple over and 

 point so as to make the part of the specific 

 inductive capacity due to the molecules of 

 opposite sign to that due to the ether. 

 Thus, for frequencies greater than that of 

 the molecules the specific inductive capac- 

 ity will be less than unity. When the 

 frequency of the force only slightly exceeds 

 that of the molecules, the effect of the ex- 

 ternal field on the molecules is very great, 

 so that if there are a considerable number 

 of molecules, the negative part of the spe- 

 cific inductive capacity due to the molecules 

 may be greater than the positive part due 

 to the ether, so that the specific inductive 

 capacity of the mixture of molecules and 



ether would be negative ; no waves of this 

 period could then travel through the me- 

 dium, they would be totally reflected from 

 the surface. 



As the frequency of the force gets greater 

 and greater, its effect in making the mole- 

 cules set will get less and less, but the 

 waves will continue to be totally reflected 

 until the negative part of the specific induc- 

 tive capacity due to the molecules is just 

 equal to the positive part due to the ether. 

 Here the refractive index of the mixture is 

 zero. As the frequency of the force in- 

 creases, its effect on the molecules gets less 

 and less, so that the specific inductive ca- 

 pacity continually approaches that due to 

 the ether alone, and practically coincides 

 with it as soon as the frequency of the force 

 is a considerable multiple of that of the 

 molecules. In this case both the specific 

 inductive capacity and the refractive index 

 of the medium are the same as that of the 

 ether and there is consequently no refraction. 

 Thus the absence of refraction, instead of 

 being in contradiction to the Eontgen rays, 

 being a kind of light, is exactly what w^e 

 should expect if the wave length of the 

 light were exceedingly small. 



The other objection to these rays being a 

 kind of light is, that there is no very con- 

 clusive evidence of the existence of polariza- 

 tion. Numerous experiments have been 

 made on the difference between the absorp- 

 tion of these rays by a pair of tourmaline 

 plates when their axes are crossed or paral- 

 lel. Many observers have failed to observe 

 any difference at all between the absorption 

 in the two cases. Prince Galitzine and M. 

 de Karnogitsky, by a kind of cumulative 

 method, have obtained photographs which 

 seem to show that there is a slightly greater 

 absorption when the axes are crossed than 

 there is when the axes are parallel. There 

 can, however, be no question that the effect, 

 if it exists at all, is exceedingly small com- 

 pared with the corresponding effect for visi- 



