204 



Professor Sihanus P. Thompson 



[May 8, 



had been working with inside the vacuum. To that question the 

 final answer cannot yet be given. Certainly some of the Lenard 

 rays resemble the interior kathode rays : but some differ in the 

 crucial respect of deflectability by the magnet. The higher the 

 degree of vacuum, the less are the rays deflected. 



Having touched all too briefly upon the researches ot Lenard, it 

 remains for me to speak of those of Wiedemann, of Erlangen, who for 

 many years has made a study both of the phenomena of electric 

 discharge and of those of fluorescence and phosphorescence. In a 

 research made in the year 1895 he attained some results of singular 

 interest. He had been making electric discharges, in collaboration 

 with Professor Ebert, by a special apparatus for producing electric 



oscillations of high frequency. This apparatus, in the modified form 

 given to it by Ebert,* stands on the table before you. It is an 

 apparatus of the same class as that described here some years ago by 

 Oliver Lodge, for producing Hertzian waves. An oscillating spark 

 is produced between two polished balls set between two condensers 

 A and B, each made of plates of sheet zinc (Fig. 7) a few millimetres 

 apart. Their external circuit is, however, led into the primary of a 

 small induction coil, the secondary of which goes to a third condenser 

 C. When spaiks from the Apps coil are sent to the spark-gap, the 

 oscillations of the two primary condensers set up secondary oscilla- 



' Wiedemann's Annalen,' hii. p. 144, 1894. 



