776 POPULAR SCIENCE MONTHLY. 



whicli have arisen in regard to this apparently new manifestation 

 of the cathode rays. In the first place, they are apparently not 

 refracted by paraffine, vulcanite, or wood, or by any substance 

 which is penetrated by them. To test this, I employed a double- 

 convex lens of wood and also a double-concave lens of the same 

 material. I placed two copper rings in the concavity of the 

 double-concave lens of wood, and also a similar copper ring out- 

 side the lens at the same height from the sensitive plate, as one of 

 the rings which rested on the wood of the lens. I also placed a 

 ring on the double-convex lens, and employed two cathodes to 

 obtain two shadows from different positions. The thickness of the 

 wooden lenses varied from half an inch to three quarters of an 

 inch. The images obtained through the wood of the lenses were 

 not distorted or changed in figure in any way by the wood, and 

 therefore no refraction could be observed by this method. On 

 account of the quick diffusibility of the rays, no accurate method 

 of determining a possible index of refraction seems possible. If the 

 photographic effect is due to longitudinal waves in the ether, and 

 if these waves travel with great velocity, no refraction would 

 probably be observed. Maxwell's electro-magnetic theory of light 

 supposes that only transverse waves are set up in the ether, and 

 no longitudinal waves exist. On the other hand, Helmholtz's 

 electro-magnetic theory of light postulates longitudinal waves as 

 well as transverse waves. The longitudinal waves travel with an 

 infinite velocity. Is it therefore possible that the X waves are the 

 longitudinal waves of Helmholtz's theory ? Our apparent ina- 

 bility to refract the rays lends color to this hypothesis. Rontgen, 

 in the preliminary account of his experiments, intimates that the 

 phenomena may be due to longitudinal waves, and in a late article 

 in the Annalen der Physik und Chemie, by Jaumann, entitled 

 Longitudinal Light, Maxwell's electro-magnetic equations are 

 modified so as to embrace the phenomenon of cathode rays ; and 

 the author shows that even Maxwell's theory can, under certain 

 conditions, give a longitudinal wave. 



The cathode rays can be deflected by a magnet, and it is said that 

 the X rays can not. It must be borne in mind, however, that when 

 the cathode rays are widely divergent it is difficult to deflect them 

 by a magnet ; the stream density, so to speak, is too feeble. The X 

 rays, therefore, may be only cathode rays modified by passing 

 through the glass vessel ; and the stream of rays may be of too 

 feeble a character to be influenced by a magnet that is, they 

 may be still cathode rays. The want of refractive power and the 

 want of magnetic action have not been fully established. Crookes 

 early showed that two cathode beams sent out from two cathodes 

 placed beside each other, repelled each other, as if they consisted 

 of streams of negatively electrified molecules. If the two beams 



