346 HERMANN VON HELMHOLTZ 



this, because I had imagined, perhaps erroneously, that the 

 theory was not yet sufficiently perfect. 



'The following seems also to point to a correspondence 

 between the two phenomena. The more the tube is exhausted, 

 the less does the magnet act upon the rays, and the more 

 rigid they become, as Dr. Goldstein expresses it. This may 

 show (although there is another possible interpretation) that 

 the magnet can only act indirectly upon the cathode rays, as 

 it does upon light, that is, by means of the ponderable matter. 

 In this case, the action of magnetic matter must be enormously 

 stronger upon the cathode rays than it is upon light, but since 

 the same difference undoubtedly exists in regard to absorption, 

 this is the less to be wondered at. 



' Generally speaking, the cathode rays excite the same fluores- 

 cence in solid bodies as does light. But I do not therefore 

 hold it necessary to assume that they are directly converted 

 into optical rays. One would be more inclined to interpret 

 the phenomenon in the opposite sense. For as the transverse 

 rays of light break up inside the bodies, they will give rise to 

 longitudinal waves, and it is quite natural according to our 

 view that these again should immediately disappear with the 

 production of the same light as is produced by the long cathode 

 rays in the vacuum. 



' I have also tried to induce phenomena of diffraction, by 

 sending thin cathode rays through a grating, but obtained no 

 result. At the same time the experiments were not of a nature 

 to prove anything. These are the kind of ideas which I have 

 on this subject. Up to the present I have not entertained any 

 hopes of utilizing the phenomena in electrodynamics, as for 

 the determination of the constant k, since the only effect that 

 can be measured exactly, the action of the magnets, appears 

 to be essentially conditioned by the ponderable substances. 

 I will reflect upon this point, and upon the objection you 

 pointed out. The latter, I think, may be entirely refuted, if 

 we succeed in obtaining more certain proof that cathode rays 

 are possible in the absence of all electrostatic differences. 



' It now only remains, hochverehrter Herr Geheimrath, to 

 repeat my sincerest and warmest thanks, and I remain, with 

 deepest respect, 



' Your devoted H. HERTZ/ 



