and the effects of lightning on H.M.S. Rodney, S^c. 123 



question whether it would strike upon the mast aXy would be 

 determined by the resistance in the direction of m y Jc, as 

 compared with that in any other direction m, B ; whether, in 

 fact, it would be easier to break down the remaining air in the 

 direction M B, or otherwise the air in the direction m y, 

 supposing the ship's mast to facilitate the progress in that 

 direction. 



17. Let the charge however strike in the direction m 3/, and 

 so fall upon the mast, — then in proceeding to its ultimate desti- 

 nation, viz. the plane of the sea B, its course is still determined 

 by the same general principles ; that is to say, it seizes upon 

 all those bodies which tend to assist its progress, and which 

 at the same time happen to be placed in certain relative posi- 

 tions, a7id upon no others, falling with destructive effect upon 

 intervening bad conductors, and exhibitiufj in non-conductino- 

 intervals all the effects of a powerful expansive force. If we 

 examine carefully the course of discharges of lightning on 

 ships in some hundred instances in which damage has ensued, 

 we shall find this effect invariable. The damage has always 

 occurred where good conductors cease to be continued, and 

 the destructive consequences most apparent are those usually 

 produced by expansion. The calorific effects, except as de- 

 pending on this cause, are really inconsiderable ; there are 

 comparatively few instances in which metallic bodies have 

 been fused, and no instance in which a bolt or chain of any 

 considerable magnitude has been even much heated. 



The following experimental and natural illustrations of these 

 facts will be found conclusive and interesting. 



Exp. 1. Lay some small detached pieces of leaf-gold a, b, 

 c, d, &c. on a piece of paper, as represented in fig. 4 ; pass a 

 dense shock of electricity over these, from the commencement 

 at A to the termination at B, so as to destroy the gold ; the 

 line which the discharge has taken will be thus shown by the 

 blackened parts ; the result will be as in fig. 5, in which we 

 perceive the course of the discharge has been in the dotted 

 line «, h, d, e,f, g, h, I, being the least resisting line ; and it 

 is particularly worthy of remark, that not only are the pieces 

 c, A- untouched, being from their positions of no use in facilita- 

 ting the progress of the charge, but even portions of other 

 pieces, which have so operated, are left perfect, as in the 

 transverse piece i and portions of a, 5, d, e, and f; so little is 

 there any tendency to a lateral discharge, even up to the 

 point of dispersion of the metallic circuit in which the charge 

 has proceeded ; indeed, so completely is the effect confined to 

 the line of least resistance, that percussion powder may be 

 placed with impunity in the interval between the portions c, d. 



