Electrical Discharge Phenomena in Rarefied Gases. 147 



" The Action of Magnetised Electrodes upon Electrical Discharge 

 Phenomena in Rarefied Gases." By C. E. S. Phillips. Com- 

 municated by Sir William Ckookes, F.E.S. Pieceived 

 February 28— Bead March 14, 1901. 



(Abstract.) 



A preliminary account of this investigation has already been laid 

 before the Society.* The present paper deals more particularly with 

 the conditions necessary for the production of a luminous ring in 

 rarefied gases and under the inflnence of electrostatic and magnetic 

 forces. 



The cause of the luminous phenomenon is traced to the action of the 

 magnetic field upon electrified gaseous particles within the rarefied 

 space, and experimental evidence is given to show that the rate of 

 change of the magnetic lines is an important factor. 



Numerous experiments relating to the loss of positive electrification 

 from a charged body when placed in a rarefied space, and in the 

 neighbourhood of a magnetic field, are also described in detail, f 



An apparatus similar to that referred to in a previous communica- 

 tion was generally found most suitable for observing the formation 

 and behaviour of the luminous ring. It consisted of a small spherical 

 glass bulb 2*5 inches in diameter, and provided with short projecting 

 necks for the purpose of carrying two oppositely placed soft iron rods. 

 These rods were pushed one through each of the short tubes, cemented 

 in position, and arranged to have their pointed ends within the bulb and 

 a sixteenth of an inch apart. 



The cores of two electro-magnets were then butted against the 

 external ends of the rods, for the purpose of magnetising them when 

 required. 



\Yhen the gas within the bulb had been rarefied to a pressure of 

 about 0*005 mm. of mercury, a discharge from an induction coil was 

 sent through it for a few seconds, the rods (now used as electrodes) 

 meanwhile remaining unmagnetised. But when the discharge was 

 stopped and the magnets were excited, a luminous ring appeared 

 within the bulb, in a plane at right angles to the magnetic axis, 

 between the pointed ends of the electrodes, and in rotation about the 

 lines of magnetic induction. 



The luminosity of the ring was found to be intermittent, its spectrum 

 showed no peculiarity, and it was not possible to obtain satisfactory 

 photographs of the revolving glow. In oxygen the ring appeared a 

 little brighter, but in hydrogen or carbonic dioxide the luminosity 

 seemed about the same as in air. 



* ' Roy. Soc. Proc.,' toI. 64, p. 172. 

 f ' Boy. Soc. Proc.,' vol. 65, p. 320. 



