108 DR. FARADAY'S EXPERIMENTAL RESEARCHES IN ELECTRICITY. (SERIES XII.) 



1416. Numerous sparks were then passed and carefully observed. They were very 

 rarely straight, but either curved or bent irregularly. In the average of cases they 

 were, I think, decidedly convex towards each other ; perhaps two thirds presented 

 more or less of this effect, the rest bulging more or less outwards. I was never able, 

 however, to obtain sparks which, separately leaving the ends of the wires n and o, con- 

 joined into one spark before they reached or communicated with the ball c. At pre- 

 sent, therefore, though I think I saw a tendency in the sparks to unite, I cannot as- 

 sert it as a fact. • • 



1417. But there is one very interesting effect here analogous to, and it may be in 

 part the same with, that I was searching for: I mean the increased facility of dis- 

 charge where the spark passes. For instance, in the cases where one end, as n, dis- 

 charged the electricity of both ends to the ball c, fig. 2., the electricity of the other 

 end 0, had to pass through an interval of air 1*5 times as great as that which it might 

 have taken, by its direct passage between the end and the ball itself. In such cases, 

 the eye could not distinguish, even by the use of Wheatstone's means*, that the 

 spark from the end n, which contained both portions of electricity, was a double 

 spark. It could not have consisted of two sparks taking separate courses, for such 

 an effect would have been visible to the eye ; but it is just possible, that the spark of 

 the first end n and its jar, passing at the smallest interval of time before that of the 

 other 0, had heated and expanded the air in its course, and made it so much more 

 favourable to discharge, that the electricity of the end o preferred leaping across to it 

 and taking a very circuitous route, rather than the more direct one to the ball. It 

 must, however, be remarked, in answer to this supposition, that the one spark between 

 d and e would, by its influence, tend to produce simultaneous discharges at n and 0, 

 and certainly did so, when no preponderance was given to one wire over the other, 

 as to the previous inductive effect (1414.). 



1418. The fact, however, is, that disruptive discharge is favourable to itself. It is 

 at the outset a case of tottering equilibrium : and if time be an element in discharge, 

 in however minute a proportion (1436.), then the commencement of the act at any 

 point favours its continuance and increase there, and portions of power will be dis- 

 charged by a course which they would not otherwise have taken. 



1419. The mere heating and expansion of the air itself by the first portion of elec- 

 tricity which passes, must have a great influence in producing this result. 



1420. As to the result itself, we see its influence in every spark that passes ; for it 

 is not the whole quantity which passes that determines the discharge, but merely 

 that small portion of force which brings the deciding molecule (1370.) up to its 

 maximum tension ; then, when its forces are subverted and discharge begins, all 

 the rest passes by the same course, from the influence of the favouring circumstances 

 just referred to ; and whether it be the electricity on a square inch, or a thousand 



* Philosophical Transactions, 1834, pp. 584, 585. 



