[ 926 ] 



LXXXIX. Rays of Positive Electricity from the Wehnelt 

 Cathode. A Preliminary Note. By Chas. T. Knipp, 

 Ph.D., Assistant Professor of Physics in the University 

 of Illinois, U.S.A.* 



[Plate XVII.] 



rilHE object of this note is to describe briefly the 

 JL work that has been in progress at the Cavendish 

 Laboratory during the past year, on the measurement o£ the 

 properties of the Canalstrahlen when a Wehnelt or hot 

 lime cathode is employed. In 1904 Professor Wehnelt f 

 observed these rays experimentally. Up to that time he 

 was not able to get a sufficiently clear outline on the screen 

 to enable him to make measurements. 



The success attending the measurement of the rays J of 

 positive electricity, in the case of an ordinary perforated 

 cathode, by putting the photographic plate inside the 

 discharge tube suggested that the same method might be 

 employed to advantage in measuring the properties of the 

 slower moving carriers that are produced by the hot lime 

 cathode. Earlier in the year numerous attempts were made 

 to get photographic records in this way but without success. 

 The inference was that if carriers are present they do not 

 possess energy enough to affect the photographic plate. To 

 overcome this difficulty I next arranged to increase their 

 velocity by means of an accelerating condenser. 



Fig-, l. 



R 



M 



tt 



flnoQ® 



The general arrangement of the apparatus is sketched 

 diagrammatically in fig. 1. It consists, briefly, of a hot 



* Communicated by Sir J. J. Thomson, F.R.S. 

 f A. Wehnelt, Ann. d. PMjs. vol. xiv. p. 464. 



t J. J. Thomson, Phil. Mag. vol. xviii. Dec. 1009 ; vol. xx. Oct. 

 1910 j vol. xxi. Feb. 1911. 



