292 On Lightning Conductors to Powder Magazines. [No. 99. 



bodies" unless those adjacent bodies are also of a metallic nature, 

 and themselves good conductors.* 



14. Dr. O'Shaughnessy states that "in Chowringhee alone, 

 in an area of one square mile, there are over 300 lightning con- 

 ductors of proper construction, yet scarcely a season passes, but 

 we hear of accidents within that area, and not unfrequently, 

 too, in houses actually provided with conductors themselves." 



15. The electrical history of such a district must be extremely 

 interesting, and it would greatly benefit science if authentic facts 



-concerning it were collected, and published. It appears that 

 Dr. O'Shaughnessy only mentions the facts upon hearsay, and 

 such evidence is not of weight enough to counterbalance the 

 direct testimony of competent witnesses, which abound on the 

 other side of the question. I have no doubt that upon proper 

 inquiry, Dr. O^Shaughnessy would find that the accidents which 

 are said to have occurred in houses actually provided with con- 

 ductors, have arisen from defective construction. 

 7 - 



16. It is not supposed that a large number of conductors will 

 avert electrical discharges from a district, though, if properly 

 constructed, they will open safe communication for their passage 

 to the earth. 



17. Dr. O^Shaughnessy thinks, that "it is altogether unne- 

 cessary either to construct lightning conductors of copper, or to 

 make them one inch in diameter," but in this opinion I have 

 again the misfortune to differ from that gentleman. The best 

 authorities have recommended a rod of an inch in diameter as 

 the standard size, experience having proved that such a rod has 

 never yet been melted by an atmospheric discharge. It is cer- 

 tainly possible that a rod of less substance might be sufficient to 

 conduct away a flash of lightning, but it is impossible to ascer- 

 tain the minimum which would suffice, without incurring the 



* I must refer the reader to the succeeding paper, for proof of the error 

 into which Mr. Daniel! has here fallen,=--W. B O'S. 



