. 
336 On Lighining-Kods. 
but one ; large ships should have one on the main-mast, and 
apother on the mizen-mast. 
t has been proposed to have conductors fixed to the surfaces 
of the masts, and the electric fluid conveyed by mean: of strips 
of metal over the deck and sides of the vessel. But this 
mode is highly ans and perhaps the best method 
yet devised, is to convey the electric fluid from the mast- 
head to the surface of the whes in a direct line, by me ns of 
a series of long copper links. Itbas come to my knowiedge 
within a few months, that a vessel in the gulf-stream wi h 
powder on board, was struck by }.ghtning and blown up, in 
consequence of the conductor not reaching th» water, having 
been /oose. and drawn on dec 
It is allowed from experiment, that the stem «f » lightning 
rod effectually defends a circle of witch it is the centre, and 
whose radius is twice its own height. According to this rule, 
a building sixty feet square requires a stem only fifteen or 
eighteen feet, raised in the centre of the roof. A building of 
one hundred and twenty feet, by the same rule, would require 
a stem of thirty feet, and such is often used; but i is better, 
instead of one stem of ¢ at length, to have two of fifteen or 
same rule should be followed for any larger or smaller build- 
ing. 
