LXII. On the Secondary Cathode Rays emitted by Substances 

 when exposed to the 7 Bays. By R. D. Kleeman, B.A., 

 B.Sc, 1851 Exhibition Research Scholar of the University 

 of Adelaide ; Emmanuel College, Cambridge *. 



§i- 



IT was discovered by Evef that a substance exposed to the 

 7 rays emits secondary cathode besides secondary 7 rays. 

 The object of this paper is to describe some experiments on 

 the amount of secondary cathode radiation from different 

 substances, as measured by the ionization these secondary 

 rays produce in air. 



Fig. 1 is a diagram of the apparatus used. The chamber 



Fio-. 1. 



Ebonite 



ElECTttOMCTEft. 



A is an ionization-chamber supported by means of a frame 

 arrangement, so that its distance from the table on which the 

 experiments were performed was about 18 cm. It consisted 

 of an aluminium box 10 cm. high, 12*5 cm. long, and 7 cm. 

 deep, with a wire gauze for its lower side. The chamber B 

 is another ionization-chamber whose electrode was. connected 

 with that of the chamber A. It consisted of a cylindrical- 

 shaped can 18 cm. in diameter and about 16 cm. high. The 

 source of 7 rays was 30 mgrm. of radium bromide contained 

 in a closed glass tube which was placed into the tubular 

 cavity of the lead cylinder 0; a plate of lead 3 mm. thick 

 placed over the opening of the cavity served to cut off the 

 (3 rays. The position of the lead cylinder with respect to 

 the chamber A was as shown in the figure. The chamber A 

 was connected to a positive potential of 200 volts, and the 

 chamber B to a negative potential of 200 volts ; and the 



* Communicated bv Prof. J. J. Thomson, F.R.S. 

 f Phil. Mag. Dec. 1904. 



