tsS 



pumj) 



r 



s 



W 



through Exhausted Tubes without Electrodes. 455 



'connected with an induction-coil, and the pressure in the 

 tube was such that the elec- 

 trodeless discharge would not Fig- 14. 



start of itself. When the coil 

 was turned on so that c was the 

 negative electrode, the elec- 

 trodeless discharge in the tube 

 at once took place, but no effect 

 at all was produced when c was 

 positive and d negative. We 

 may thus regard the effect pro- 

 duced by the presence of a con- 

 ductor as due to the conductor 

 catching the tubes of electrostatic 

 induction, and concentrating 

 them on the discharge-tubes. 

 These tubes in many cases 

 acting indirectly by producing 

 a glow-discharge through the 

 tube, which, by diminishing the 

 electric strength of the gas, 

 makes discharges of any other 

 kind very much easier. Though the presence of a conductor 

 near the discharge-tube will, in general, concentrate the tubes 

 of electrostatic induction on the discharge -tube more than 

 would otherwise be the case, yet this does not always happen. 

 When in some positions the conductor may hold back for a 

 time from the discharge-tube tubes of electrostatic induction 

 which would otherwise pass through it, and thus diminish the 

 maximum density of the tubes of electrostatic induction in 

 the discharge-tube, and hence tend to stop the discharge. I 

 have frequently met with cases where the presence of a con- 

 ductor diminishes the intensity of the discharge. One of the 

 most striking of these is when the two jars are insulated, and 

 a square discharge-tube used. The spark was adjusted so 

 that the discharge just, but only just, went round the tube. 

 A sphere connected to earth was then moved round the dis- 

 charge-tube; in some positions it increased the brilliancy of 

 the discharge, and the tube became quite bright, while in 

 other positions it stopped the discharge altogether. 



The observation of the behaviour of the discharges through 

 these tubes is a very convenient method of studying the effect 

 of conductors in deflecting the flow of the tubes of electro- 

 static induction which fall upon them; for the appearance of 

 the discharge is affected not merely by the average, but also 

 by the maximum value of the electromotive intensity which 



