1896.] 



27 



That the Rontgen rays possess three characteristics of ordinary light ; 

 viz., rectilinear propagation, as shown by their ability to cast shadows ; 

 the power of producing fluorescence ; and the power of effecting chemical 

 decomposition in a sensitive photographic plate. They difter from light, 

 however, in nearly all other respects. If they are ether waves they may 

 be transverse waves, which we know of; or they may bethelong-looked- 

 for longitudinal waves. They are, however, apparently incapable of re- 

 flection, refraction or interference, all characteristic of transverse vibra- 

 tions. If they are transverse vibrations they belong to some part of the 

 spectrum that we have not hitherto studied. In the opinion of some phys- 

 icists they belong to a region considerably below the red ; in the opinion 

 of others they are exceedingly short wave lengths, possibly approaching 

 atomic or molecular dimensions. 



I have used in connection with my colleague, Dr. Kennelly, in the 

 study of the Rontgen effect, both the character of apparatus described by 

 Prof. Goodspeed, as well as other apparatus. Dr. Kennelly and I, charge 

 a battery of Leyden jars with the discharge of a large Ruhmkorft' coil ; 

 we get a spark discharge and a spark gap, and then use that spark dis- 

 charge, which is an oscillatory discharge, through the primary of a Tesla 

 coil. We thus obtain in the secondary coil an exceedingly high discharge 

 and use this to excite the Crookes tubes. The Tesla coil was immersed 

 in rosin oil. It seems from the experiments we have made that these 

 very rapid oscillations are not so apt to injure the tube and apparently 

 produce better results. However, in sharp opposition to this, I hear a 

 rumor, though it is only a rumor, that at the Johns Hopkins University 

 they are working in the opposite direction ; viz., with very few oscilla- 

 tions of the primary per second. I hope Prof. Rowland, who is conduct- 

 ing these experiments, will soon let us know what he is doing. 



Mr. Edison has been a tireless investigator in this field of physical re- 

 search. 



Prof. Schuster is decided in his opinion that the Rontgen rays are not 

 the cathode rays. He agrees that the point of origin is where the stream 

 of negatively charged molecules strikes the glass. Prof. Whiting finds 

 gum to be the most transparent and rock salt the most opaque substance 

 to the action of the rays. Prof. J. J. Thompson states that the cathode 

 rays are incapable of affecting sensitive photographic plates. We all know 

 that the ultra-violet rays, which some think are the same as the Rdutgen 

 rays, will effect the discharge of a negatively excited body. Prof J. J. 

 Thompson has shown that the Rontgen rays will effect the discharge of 

 either a negatively or a positively excited body, and this whether or not 

 the body is surrounded by the highest insulating substances known to the 

 electrician, like vulcanite or parafine. Of course, I know that most of 

 you will know what this means ; viz , that a leak takes place in those 

 substances ; or, in other words, that while the Rontgen rays are passing 

 through these substances they become conductors of electricity. 



