1840.] On Lightning Conductors to Powder Magazines. 301 



windward, and was secured by copper strips to the ship's side. 

 A flash strikes the top, and a flash is seen by all on board, at 

 the same instant, to leave the conductor about on a level with 

 the cap of the main-mast, and to dart into the water over the 

 lee bulwarks. This is a clear instance of an excess of electri- 

 city leaving a conductor through which it cannot force an 

 instantaneous passage. All that the conductor could convey 

 was borne off to windward — the rest opened to itself another 

 and less difficult route. 



24. It might here be the most appropriate place to discuss the 

 question, What is the greatest mass of metal a flash of lightning 

 can fuse ? — When we remember that the surface of a cylinder 

 increases by a simple multiple of the diameter, while the mass 

 increases as the cube — that every fact shews it to be the surface 

 which the electricity pursues,* while its calorific effect must 

 be in the inverse proportion to the mass — it will probably seem 

 that the surface may be too small to convey a given quantity of 

 electricity, although this be insufficient to melt or even to heat 

 the whole mass of the metal. 



25. Mr. Daniell, in reference to the efficacy of single con- 

 ductors, enters on the much disputed question, as to whether 

 these attract lightning, or are merely passive conductors for 

 its conveyance. He takes the latter view, declares the former 

 to be absurd^ and compares the conductor to a water- 



* Mr. Harris, a high, authority on electricity, makes these remarks re- 

 specting the surface action of conductors : — 



" The conducting power of a metallic rod has but little relation to its 

 solid contents, but is principally dependent on its surface, from which cause 

 the mere gilding of a ball of wood is found to conduct a proportionate 

 electrical discharge with the same facility as if the ball was a solid mass of 

 metal, hence a less quantity of metal formed into a hollow tube would 

 be as a conductor, even more effectual than a solid rod of the same diameter, 

 because its superficies would be increased !" Harris on Electrical Conductors, 

 p. 31. 



f The Board are referred to the marginal note at para. 17, for Mr. 

 Daniell 's own admission, that pointed conductors " draw off " a considerable 

 portion of electricity, &c. &c. Drmving off and " attracting" are very like 

 synonymous terms.— W, B. OS. 



