662 FHILOSOPHICAL TRANSACTIONS. [aNNO I762. 



with those bright lights, which our mariners call comazants, and are the feu St. 

 Elme of the French, and w*ere the Castor and Pollux of the ancients, is within 

 the sphere of action of a thunder cloud. Anciently, when these were seen, they 

 were only considered as the attendants of a storm, and no consequence was drawn 

 from them ; but now, (since Dr. Franklin's admirable discovery of conducting 

 lightning from the clouds, we know them to be no other than a modification of 

 the same meteor, which constitutes thunder and lightning) they demonstrate 

 that danger is near, and therefore we should do our utmost to prevent its effects. 

 This in Dr. W.'s opinion would be done, if a wire of iron or any other metal 

 were connected with the spindles and iron work at the tops of masts of ships, 

 and conducted down the sides of the masts, and from thence in any convenient 

 direction so disposed as always to touch the sea-water. By these means, the ac- 

 cumulation of the matter of thunder and lightning will be prevented, to a consi- 

 derable distance from the ship, by its being discharged silently by the wire, 

 which will not be done by the masts; as these from their height, figure, and con- 

 stituent parts, without an apparatus of this kind, tend to direct and conduct the 

 lightning into the ship. But for a further explanation on this head. Dr. W. re- 

 fers to p. 215, vol. 48 of the Phil. Trans., where he had considered this matter 

 more at large. 



The applying wire to the masts of ships will be neither difficult nor expensive ; 

 as a brass wire of the thickness of a large goose quill, will in most cases be large 

 enough to answer this purpose. He prefers brass wire to iron, as less liable to 

 rust ; and any metal corroded by rust, to the centre, ceases to be of any use in 

 directing the lightning, in the degree hoped for and expected by this apparatus. 

 He declines entering into a minute detail o( the rationale of this process ; but 

 from analogy only he mentions that the same quantity of gunpowder, which con- 

 fined in a close place, will throw down a tower, or rend a rock, will, when fired 

 loose in the open air, be almost inoffensive. 



Thunder storms are very frequent and severe in Pennsylvania, and great mischiefs 

 often happen from them ; Dr. W. was informed by Dr. Franklin, that since an 

 apparatus of the kind above mentioned, placed at the tops of the houses, has b*^en 

 generally used at Philadelphia, not a single instance of mischief from lightning 

 had happened in that city. He informs further, that at Philadelphia in a thun- 

 der storm, the lightning was seen to strike the ridge of a house, on which an 

 apparatus of this sort was erected. The lightning, like a ball of fire, ran from 

 the ridge of the house to the apparatus, and in running down, it melted the con- 

 ducting wire, without doing any damage to the house. This shows the expedi- 

 ency of applying either large wires or small rods, in which the melting will most 

 probably be prevented ; notwithstanding it has been repeatedly found, that 



