Mr Owen, Magnetic Deflexion of the Negative Current. 493 



On the Magnetic Deflexion of the Negative Current of Electricity 

 from a hot Platinum Wire at low pressures. By Gwilym Owen, 

 B.A., Christ's College. 



[Received 30 May 1904.] 



It has long been known that the space surrounding an incan- 

 descent platinum wire conducts electricity. McClelland * has 

 shown that this is due to two causes — 



(a) I 1 © the ionisation of the gas in contact with the wire. 



(b) To the emission of ions from the metal. 



This electrification is a most complicated effect, depending on 

 the nature and pressure of the gas surrounding the wire, on the 

 gas absorbed by the metal, on the temperature and previous 

 treatment of the metal and other not yet fully-known causes. 



These effects are somewhat simplified in the case of a wire 

 glowing at very low pressures. 



The discharge from hot platinum has been made the subject 

 of experiment by very many observers. The most recent work is 

 that of Dr H. A. Wilsonf and Mr O. W. Richardson J. 



In the Philosophical Magazine for December, 1899, Prof. 

 J. J. Thomson describes a method for determining the ratio of 

 the charge e to the mass m for the carriers of the negative 

 electricity discharged from metals at low pressures. This ratio 

 has been determined by Prof. Thomson for the carriers of the 

 negative electricity discharged by an incandescent carbon fila- 

 ment, and for the carriers of the positive electricity from glowing 

 platinum. The carriers of the negative electricity at low 

 pressures have been shown to be corpuscles, whereas the carriers 

 of the positive electrification are particles of molecular di- 

 mensions. 



Now it is well known that when a platinum wire is heated in 

 air it loses weight, showing that particles of platinum are driven 

 off. The writer has shown (Phil. Mag., Sept. 1903) that this 

 disintegration of the platinum takes place in air at a temperature 

 as low as 200° C. Child § in his experiments on the discharge 

 from hot platinum wires also obtained evidence that particles 



* Proc. Camb. Phil. Soe. x. p. 241, 1900. 



t Phil. Trans. A, 202, pp. 243—275, 1903. 



J Proc. Camb. Phil. Soc. xi. p. 286, 1901 ; Phil. Trans. A, 201, pp. 497—549, 1903. 



§ Physical Review, April 1902. 



