359 Lightning Conductors in Ships. 
21. It will be found, however, that the action of pointed metallic 
bodies is purely passive ; that they only afford by the aptness of their 
parts an easy transmission to the electric matter; so that they can no 
more be said to attract the matter of lightning, than a dike can be said 
to attract the water which necessarily flows through it at the time of 
heavy rain; and, as in the one case, the water is drawn down by a 
force not peculiarly appertaining to the dike, so, in the other case, 
the electric matter is determined to a given point, in a somewhat simi- 
lar way, by a force not appertaining to the metal. Moreover, it may 
still further be reasoned by analogy, that, as the quantity of water 
transmitted will depend on the capacity of the dike, and the final 
protection it gives in conveying the fluid on the length to which it is 
continued ; so, on the other hand, the protection afforded by a light- 
ning-rod will also depend on its capacity, and the distance to which 
it runs. If, in both cases, the length be extended until the force in 
action be satisfied, the protection received will be as the capacity for 
transmitting the current: if both be perfect, the protection will be 
complete ; if the dike be not present, the water must be supposed 
to run loose and undirected ; or, if its continuity be frequently inter- 
rupted or narrowed to a small compass, the damage must then be 
supposed to happen in the intermediate spaces. Such is, in fact, the 
way in which all bodies of the conducting class already mentioned 
(4) operate in conveying electrical discharges; and it must never be 
forgotten as an important feature in this discussion, that, whenever 
we erect an artificial elevation on the earth’s surface in the ordinary 
way, we do, in fact, set up a conductor of electricity, upon which 
the electricity of the atmosphere will fall, and no human power can 
prevent it. Hence, if metallic bodies be present, those will be first 
assailed; if not, then the electric matter will fall on the bodies next 
in conducting power, and so on. 
22. A curious illustration of this principle will be found in sa = 
tract from the Memoirs of the Count de Forbin, which is given ™ 
the forty-eighth volume of the Philosophical Transactions. “In 8 
night,” says the author of these memoirs, “it became extremely dar ; 
and it thundered and lightened dreadfully. As we were threaten? 
with the ship being torn to pieces, I ordered the sails to be taken - 
We saw upon different parts of the ship above thirty of St. eck? 
fires; amongst the rest there was one upon the top of the vane ° 
the main-mast more than a foot and a half in height; 1 ordered one 
of the sailors to take it down. When this man was on the top, : 
