1894.] 



on Electric Discharge through Gases. 



245 



and while doing so gives out a phosphorescent light. It is in accord- 

 ance with this that at a high temperature where ozone cannot exist 

 a discharge through an oxygen bulb does not show any glow. 



I said at the beginning of this discourse, that gases were ex- 

 ceedingly good conductors of electricity. I will now endeavour to 

 show an experiment which proves that statement. The apparatus 

 which I shall use for this purpose is a slight modification of the one 

 I have used for producing the ring discharge ; the only difference is 

 that in the wire connecting the two coatings of the jars there are 

 two loops instead of one. In one of these loops an exhausted bulb 

 is placed to serve as a kind of galvanometer ; the brightness of the 

 discharge is an indication of the strength of the current flowing 

 round the coil. If 1 place a second conductor in the other loop, 

 currents will be started 



in it and part of the i Fl £ * 



energy of the discharge 

 will be absorbed ; this 

 will leave less energy 

 available for the bulb 

 in the first, so that the 

 discharge in this bulb 

 will be dimmer. The 

 effect produced on the 

 discharge will depend 

 upon the conductivity 

 of the substance placed 

 in the second loop. 



The effect is not 

 directly proportional to 

 the conductivity, in 

 fact, a perfect conductor 

 would not produce any 

 diminution, nor would an 

 absolute non-conductor; 

 for a given period and 

 with apparatus of given dimensions, there is a certain conductivity 

 which gives a maximum effect ; this follows easily from the theory of 

 induction of currents, but at this late period in the evening I will 

 take a shorter course and prove it by an experiment. 



I put a piece of brass in this loop, and you see it produces but a 

 small effect upon the brightness of the discharge. Instead of brass, 

 I now insert a plumbago crucible, which, though a conductor, is not 

 nearly so good a one as the brass, and you see the discharge in the 

 indicating bulb is completely stopped. 



I will now place in the second loop an exhausted bulb ; you see 

 it produces a decided diminution in the intensity of the discharge in 

 the galvanometer bulb. I now replace the bulb by another of the 

 same size containing dilute sulphuric acid ; you see it does not 



