DISCHARGE (JF ELECTKICITY. 



243 



the si)ark leiigtli in the piiniary circuit may be «o adjusted tli.it a dis- 

 cliarge passes when there is a clear way round the tube, l»ut st()[)s 

 when a pellet of mercury is forced up so as to close tlie 

 yanjiway. I noticed a similar effect in my experiments 

 with a lonji' va<'uum tube described in the ProceediiH/.s of 

 the Ti'oi/al Socictj/ for .lanuary, 1801. 



I had another discharge tube })repared, of whicli a sec- 

 tion is shown in Fig. S, a-, in which a diaphragm (AB) of 

 thin cop])er plate was placed across the tube; the diaphragm 

 ha]»]>ened to catch at the bottom of the tube, so that it 

 divided the latter rather unequally, and left a luirrow pas- 

 sage round its edge. As much of the discharge as thert; 

 was room for went round the edge of the i)late; the remain- 

 der was not able to get through the copper, but formed a 

 closed circuit by itself in the larger segment of the tube. 

 In aiu)ther tube, which is represented in section in Fig. 8, /i, ^"'- ' 

 the copper diapliragm was attached to the walls of the tube by sealing- 

 wax, so that there was no free way; in this case the discharge again 

 refused to go through the copper, and split up into two sei)arate dis- 

 charges, as in the figure. AVheu the tube was divich-d by copper 

 diaphragms into six segments, as in Fig 8, ?/, no discharge at all would 

 pass through. When the primary was slipped up the tube above the 

 diaphiagni, a brilliant discharge was obtained. These four experi- 

 ments all illustrate the difficulty which the electricity has in getting 

 transferred from a gas to another conductor. 



Fl(i. H. 



There is do discharge through the secondary, if it is of such a kind 

 (hat, considering a closed curve drawn in it, the electro-motive inten- 

 sity as we travel along the curve tends to polarize the i)articles in one 

 half of the chain in onc^ direction, and in the other half in tlie opposite 

 direction, the direction being reckoned relative to the diiection we are 

 traveling round the curve. Thus for examjde if we take a tube 

 whose axis is bent back on itself, as in the figure, the electro-motive 

 inti'nsity Avill tend to iK)larize the particles in one ])art of the chain in 

 the direction of the arrow, and those in the other in tlie opposite 



