1894] 



on Electric Discharge through Gases. 



247 



the mercury so as to increase the pressure of its vapour, a bright 

 discharge passes through the outer layer, while the inner bulb is 

 quite dark ; the outer layer is now a conductor, and by its action 

 screens off from the inner bulb the induction of the coil. 



The last experiment I have to show is one on the effect produced 

 by a magnetic field on the 



discharge. When the dis- Fi g 6 ■ c 



charge has to flow across the 

 lines of magnetic force, the 

 pressure of the maguetic field 

 retards the discharge ; when 

 however, the discharge flows 

 along the lines of magnetic 

 force, the discharge is helped 

 by the magnetic field. This 

 is shown in the following 

 experiment. A is a bulb; 

 B a square tube, one side of 

 which is placed between the 

 poles of an electromagnet ; 

 the coil C, which connects 

 the outside coatings of the 

 jars, can be adjusted so that . 

 when the magnet is " off," L. 

 the discharge passes through 



the bulb but not round the square tube ; when, however, the magnet 

 is " on," the discharge passes in the square tube but not in the 

 bulb. In the square tube the discharge passes along the lines of 

 magnetic force and is helped ; in the bulb it passes across them 

 and is retarded. 



[J. J. T.] 



