l!22 Mr. Snow Harris on Lightning Conductors 
14. Any continuous metallic rod or other body, m n (fig. 2.), 
connected with the lower plane, must be considered merely 
as a passive Vv^ay of access for the charge so far as it goes ; 
the electrical agency being observed to seize upon substances 
best adapted and in a position to facilitate its progress, or 
otherwise to fall with destructive effect upon such as resist it. 
15. It is easy to perceive here, that the presence of a con- 
ducting rod, m n (fig. 2), or other conducting body, has no- 
thing whatever to do with the great natural action set up be- 
tween the planes A B. It is in fact to be considered merely 
as a point in one of them. The original accumulation of elec- 
tricity and subsequent discharge, would necessarily go on 
whether such a rod were present or not, as is completely shown 
by experience. When present, its operation is confined to the 
transmission, so far as it extends, of that portion of the charge 
which happens to fall upon it; and since it is quite impossible 
to avoid the presence of conducting bodies in the construction 
of ships, it is the more important to understand clearly in what 
way damage by lightning occurs to the general mass, and how 
it may be best avoided. 
16. When discharges of lightning fall upon a ship in the 
way above stated, as being a heterogeneous mass fortuitously 
placed between the charged surfaces A B (fig. 3.), the course 
of the discharge is always determined through a certain line 
or lines, which upon the whole least resist its progress. The 
interposed air between the ship and the clouds first gives way 
in some particular point, probably the weakest, — suppose at 
A, fig. 3 ; — the electrical agency then meeting with continued 
resistance from the non-conducting particles of air, is often 
turned into a tortuous course. Suppose it arrives in this 
way at some point, in the vicinity of a ship at the 
be accumulated on thick glass or on thin, the result is the same ; it is merely 
the intensity as indicated by the electrometer which changes. 
Now the term free electricity, applies to the greater or lesser influence 
of the opposed coating in respect of other bodies. In the case of the op- 
posed surfaces of the clouds and earth, all the charge is necessarily free 
electricity, since there exists no other point upon which it can tend to dis- 
charge. In the same way the electricity of the jar, when the coatings are 
very near, is nearly all redundant, or free electricity, in respect of the ac- 
tion between them, although latent in respect of other bodies. Hence with 
a moderate accumulation, the electrometer exhibits but a small intensity, if 
any. The only difference at the time of the discharge, is in the position of 
the discharging circuit, which in the case of the clouds and sea, is directly 
in the interval of separation; and as we find the principle of induction al- 
ways active in cases of lightning, the thickness of the stratum has evidently 
no influence on the conditions of the accumulation, especially when we 
consider the great extent of the opposed surfaces, which may possibly be 
20,000 or more square acres. Dr. Faraday has shown that no distance 
excludes the inductive action. 
