336 On Lightning-Rods^ 



but one ; large ships should have one on ihe main-mast, and 

 another on tlie raizen-mast. 



It has been proposed to have conductors fixed to the surfaces 

 of the masts, and the electric fluid conveyed by means of sitrips 

 of metal over the deck and sides of the vessel. But this 

 mode is highly objectionable; and perhaps the best method 

 yet devised, is to convey the electric fluid from the mast- 

 head to the surface of the water, in a direct line, by me ns of 

 a series of long copper links. It has come to my knowledge 

 within a few months, that a vessel in the gulf stream wi h 

 powder on board, was struck by lightning and blown up, in 

 consequence of the conductor not reaching th water, having 

 been Loose, and drawn on deck. 



It is allowed from experiment, that the stem f n lightning 

 rod efl:ectually defends a circle of wliich 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 centr- 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 t at length, to have two of fifteen or 

 eighteen feet, one being erected thirty feet from one end of 

 the building, the other at the same distance from the other 

 end. and consequently sixty feet from each other. The 

 same rule should be followed for any larger or smaller build- 

 ins. 



