402 



Mr. V. E. Pound on the Secondary Hays 



the tube E was closed by means of a thin brass sheet, and a 

 flat circular plate, K, of carbon or metal was held against 

 this thin brass sheet, by means 



-bis-. 1. 



n 



n 



of a flanged collar F provided 

 with a screw. The distance 

 between the polonium and 

 the lower face of the carbon 

 or brass plate was "6 cm. 

 The whole apparatus was 

 connected by a tube G to a 

 Graede pump and a McLeod 

 gauge. The apparatus was 

 insulated by mica and sup- 

 ported in such a way that 

 the polonium and the cir- 

 cular plate opposite the polo- 

 nium were symmetrically 

 placed between the poles of 

 a powerful electromagnet. 

 The circular plate held at F 

 could be altered in tempe- 

 rature by liquid air or some 

 other liquid of constant tem- 

 perature in the tube E, The polonium was connected by 

 means of the brass rod B and a screened connecting wire to 

 an electrometer of moderate sensibility. 



to earth 



to electro meter 



3. Experiments with Carbon at Different Temperatures. 



The method of conducting the experiments was as follows. 

 The carbon plate K was charged to a negative potential of 

 about 80 volts by connecting the outer part of the apparatus 

 to a battery. This high negative potential on the carbon 

 was sufficient to prevent any 8 rays from leaving the polonium. 

 The Graede pump was set exhausting the gas from the appa- 

 ratus, and seven minutes after the pump was started the 

 pressure of the gas was read by a McLeod gauge, and the 

 rate of charging of the polonium was measured by the elec- 

 trometer. The charge which came to the polonium was 

 negative, and consisted of a current of a rays leaving the 

 polonium, a current of secondary rays coming from the 

 carbon to the polonium excited by the « ray bombardment 

 on the carbon, and an ionization current through the re- 

 maining gas in the chamber. Readings of the charge which 

 accrued on the polonium plate were made at definite intervals 

 of time afterwards until the rate of charging of the plate 



