Lightning Conductors to Powder Magazines. 433 



the conclusion that the electricity passing through it was greater in 

 quantity than it was efficient to discharge, is warranted by the facts 

 stated. Other facts advanced by Dr. O'Shaughnessy in his second report, 

 appear to us decisive as to the possibility of a charge quitting a con- 

 ductor after it has become engaged in it, but we conceive too much has 

 been based on the solitary case, above alluded to, and there exist 

 imperfections in the details, which it would have been preferable to 

 have avoided. We are ignorant of the dimensions, the material, and 

 the underground arrangements of Mr. Trower's conductors, so that we 

 are at a loss to estimate fully and perfectly its efficiency, and to compare 

 it with the standard conductors recommended by Faraday and Daniell. 

 We feel assured however, we have only to express our sense of the 

 imperfection of Dr. O'Shaughnessy's details, in this instance, to insure 

 his furnishing us many future communications with the fullest in- 

 formation available. 



With reference to the third objection specified by Dr. O'Shaughnessy, 

 viz. the danger from the lateral discharge, Dr. Faraday conceives that 

 with a well arranged conductor it would be so slight as scarcely to 

 merit attention. He admits however that the existence of portions of 

 metal, as bolts, bell wires, &c. within a building, may, by establishing 

 imperfect conducting trains from the exterior to the interior, give rise 

 to lateral sparks when the conductor is struck ; and Dr. O'Shaughnessy 

 has very correctly pointed to the copper linings of the powder barrels 

 as furnishing such trams. The existence of these appears to us to add 

 much to the force of Dr. O'Shaughnessy's third objection, since in a well 

 stored Magazine, the quantity of copper is very great, and the recipro- 

 cal action between it and the charged conductor may certainly be of 

 sufficient intensity to give rise to serious consequences. To do away 

 with these metallic linings, would enable us to fulfil the conditions 

 required by Dr. Faraday for the perfect safety of our Magazines, and 

 we are not aware of their being so absolutely essential to the pre- 

 servation of the powder from injury or accident, that it would be 

 impracticable to substitute some non-conducting substance for them. 

 Were this to be done, we cannot conceive any danger arising from 

 lateral discharge, since the whole of the materials subjected to the 

 inductive influence of the charged conductor would be non-conducting 

 substances, and a solid mass of masonry, seldom less than four feet in 

 thickness, would be interposed between the inducing agent and the 

 inflammable matter. Having thus shewn that none of the objections 

 seated by Professor O'Shaughnessy have proved sufficiently powerful to 

 induce Dr. Faraday to alter his opinion as to the perfect efficiency of 



