754 

 a 



bir 



J. J. Thomson on 



nd then travel between the poles MM of an electromagnet 

 ind the parallel plates PP which are connected with a battery 



Ear. 2. 



of small storage-cells ; the rays after being deflected fall on 

 the willemite screen S. With a tube of this kind the appear- 

 ance on the screen as the pressure is gradually reduced is as 

 follows, the rays being exposed to both magnetic and electric 

 forces. At the highest pressure at which the phosphorescence 

 is visible, the phosphorescent, patch covers a considerable 

 area, the left hand (the least deflected) boundary being fairly 

 well defined while the other boundary is hazy. As the 

 pressure is still further reduced we get the appearance shown 

 in fig. 1 ; this persists for a considerable range of pressure, 

 but as the pressure is still further reduced bright spots as 

 described in my paper (Phil. Mag. [6] xiii. p. 5G1, 1907) 

 begin to appear, while the luminosity appears to divide into 

 two portions, the appearance being that represented in fig. 3. 



The luminous band, which at the higher pressures was the 

 sole representative of the phosphorescent, can still be seen in 

 its old position though it is not so bright as when the pressure 

 was higher, the negative continuation of it still persists. As 

 the pressure is still further diminished this part of the phos- 

 phorescence with its negative accompaniment gets fainter 

 anc fainter but does not alter in position, showing that the 



