and the effects of lightning on H,M,S. Rodney, ^c. 123 
question whether it would strike upon the mast at y would be 
determined by the resistance in the direction oi m y 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 y, 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, and upon no others, falling with destructive effect upon 
intervening bad conductors, and exhibiting in non-conducting 
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, h, 
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 a, 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, k 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, h, d, e, and 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. 
