224 Prof. 0. J. Lodge on the Theory 



several thousand ohms would offer to a steady current of cor- 

 responding strength ; the actual obstruction being given by- 

 equation (8'). 



Another way of putting the matter, is to say that for the 

 first few oscillations the damping term, e~ mt in equation (3), 

 has no appreciable effect ; and that, accordingly, the E.M.F. 

 applied to the conductor alternates rapidly from V to — V 

 and back again. 



But Y is the initial potential of the condenser, diminished 

 (so far as the conductor is concerned) by the E.M.F. needed 

 to jump whatever thickness of air it has jumped before reaching 

 the conductor. Hence this V may be something quite com- 

 parable to the potential needed to jump through air all the rest 

 of the way, and it may depend on a mere nicety whether it 

 prefers the conductor or not. 



Thus arises the difficulty experienced in helping a jar to 

 overflow by means of discharging-tongs brought near the two 

 coatings. Sometimes the flash will make use of the tongs, 

 sometimes it will prefer to go all the way through air; the fact 

 being that the obstruction offered by a metal requires a large 

 portion of the potential needed to break through a corre- 

 sponding length of air. Undoubtedly the metal rod offers 

 some advantage ; but it is much less than has been usually 

 supposed. 



During the instant of discharge, therefore, the upper part 

 of a lightning-rod experiences enormously high potentials in 

 alternately opposite directions. Any conductors in the neigh- 

 bourhood may easily receive side flashes, and even the bricks 

 into which its supports are driven may be loosened and dis- 

 turbed ; and all this quite irrespective of any question as to 

 the goodness or the badness of the " earth." It becomes, 

 therefore, quite a question whether it is not, after all, advisable 

 to try and confine the discharge to the conductor by means of 

 insulators, or whether it is better to reduce the excessive po- 

 tential by lateral extensions of considerable static capacity. 

 The advantage of sharing the discharge among a number of 

 well- separated conductors, instead of concentrating it all in one, 

 is obvious. 



Theory of Experiments on u Alternative Path" 



In a lecture to the Society of Arts (see Journal of the Society 

 for 22nd June 1888, reprinted also in i Electrician, 29th June 

 1888), I describe some experiments I have made on the E.M.F. 

 needed to force a discharge through various conductors, by 

 seeing what length of air-space it will prefer to jump. The 

 original potential of the condenser being able to jump, say, two 



