116 Mr. Snow Harris on Lightning Conductors 



fessor's observation of the effect of nitrate of mercury in 

 preserving the inactive state ; but it was also necessary to 

 protect the wires at and above the surface of the acid from 

 the corroding action of its fumes by a coating of wax or glass. 

 By these means the inactive condition of the iron was main- 

 tained ; but another obstacle then arose in the crystallization 

 of nitrate of mercury, by which the cells after twenty or thirty 

 hours' use were generally broken ; and this could not be sur- 

 mounted but at the sacrifice of some power, by diluting the 

 acid, which the presence of the nitrate permitted, and the 

 substitution for the cells of pipe-clay of others made of wood. 



I cannot give comparative results obtained with iron and 

 platina batteries, but I may mention that with an arrange- 

 ment of six cylinders of sheet iron, each containing thirty-six 

 square inches in strong nitric acid, without mercury, and as- 

 sociated with zinc plates of half their size, a current was evolved 

 which for several hours ignited charcoal, or the whole of a 

 strip of platina six inches in length by one-eighth of an inch in 

 width. The construction of this battery was imperfect in se- 

 veral respects, particularly in the porous vessels being much 

 too thick ; there is, therefore, reason to suppose that an equal 

 power might' have been obtained from a less number of cells. 

 As some progress in advance of the Professor's experiment 

 in which the current ceased with the solution of the film of 

 peroxide of lead, this communication may possibly be deemed 

 worthy of being recorded: but the importance of my results 

 in relation to the proposed object of the experiments is, I 

 think, materially affected by the discovery of Mr. Cooper, as 

 given in your last Number, of the application of charcoal and 

 other forms of carbon as a substitute for platina in the voltaic 

 arrangement of Mr. Grove. 



I have the honour to be. Gentlemen, &c. 



52, King's Road, Brighton, ThoMAS Hawkins. 



Jan. lOth, 1840. 



XX. On Lightning Conductors^ and the Effects of Lightning 

 on Her Majesty^ Ship Rodney and certain other Ships of 

 the British Navy : being a further examination of Mr. 

 Sturgeon's Memoir on Marine Lightning Conductors. By 

 W. Snow Harris, Lsq..^ F.R.S., Sf-c. 



[Illustrated by Plate T.] 

 To the Editors of the Philosophical Magazi7ie and Journal. 

 Gentlemen, 

 1. TN my former communication (L. and E. Phil. Mag. vol. 

 -*■ xiv. p. 461.) I considered the nature of a well-known 



