481 



KEPORT — 1891. 



it is alternating ; in fact, I first noticed the effect when using a battery 

 made up of a very large number of storage cells. 



The apparatus consists of two equal bulbs, connected by a glass tube, 

 ■which is open originally but afterwards fused up : one of the bulbs 

 contains carefully prepared phosphorus pentoxide, the other is empty of 

 all but gas. The two bulbs were exhausted by an air-pump until the 

 pre.ssure of the gas in them was very low. They were then sealed off from 

 the pump, and the passage between the bulbs was fused up. In this way 

 the two bulbs are filled with the same kind of gas at the same pressure ; 

 the gas in one bulb will, however, gradually become dry, while that in the 

 other will I'emain in its original damp condition. Just after the opening 

 between the bulbs was fused up, the discharge passed freely through either 

 bulb when placed inside the coil. After the apparatus had stood for some 



Fig. 1. 



e 



9 



days lon» enough for the gas in the bulb containing the phosphorus pent- 

 oxide to become dry, the two bulbs showed a marked difference in their 

 behaviour when placed inside the coil. The discharge, as you see, still 

 passes freely in the damp bulb ; but not the faintest trace of discharge can 

 be detected inside the dry one, and even when the distance between the 

 terminals of the Wimshurst machine is increased far beyond that neces- 

 sary to produce a discharge in the damp bulb, the dry bulb still remains 

 free from dischar<^e. It is thus evident that, to start a discharge in the 

 dry <'as, a much larger electro-motive force is required than is necessary to 

 produce the same effect in the damp gas ; in other words, the presence of 

 aqueous vapour facilitates to a great extent the passage of tlie discharge. 



If however, I produce a brush discharge in the dry bulb by bringing 

 to the outside of the bulb a wire connected with the high potential pole 

 of the Wimshurst machine, the ring discharge will start at once in the 

 dry bulb, and after it has once been started an electro-motive force, very 



