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



of facts will doubtless be thus quickly accumulated, and from 

 these we may reasonably hope to found certain opinions on 

 the points still open to doubt and discussion. 



48. The electrical history of Chowringhee I will take care 

 to collect for Mr. Darnell's gratification, with the precision 

 he is good enough to recommend me to observe. I only regret 

 that this is not the appropriate place for noticing the very 

 courteous remark he has made upon this topic. 



49. I designedly forbear from all observations on the attach- 

 ment of conductors to ordinary edifices, whether private or 

 public. No one is more convinced of their value than I am, 

 but I am at the same time as satisfied that as they are usually 

 constructed they are sources rather of danger than of pro- 

 tection; referring therefore, with great respect, to my first 

 report, I can only modify the suggestions therein given to the 

 extent, that I believe six to ten feet interval between the walls 

 of the magazine and the conductor will suffice, instead of the 

 more considerable space I first recommended. With this 

 sole exception, I am deeply impressed with the belief that 

 it were wiser to commit our magazines to the same chances 

 through which they have passed unharmed for the last half 

 century, than expose them to the possible dangers I have 

 described to proceed from the attachment, in the ordinary 

 manner, of an inadequate number of conductors erected at 

 but one foot from their walls. 



50. To economize materials, it would be advisable to erect 

 a wall as high as the roof of the magazine, ten feet distant 

 from it all round. At each corner of this wall a conductor 

 twenty feet higher than the roof should be placed, and pro- 

 perly led to the ground as deep as the water level. Between 

 these conductors, at every ten or fifteen feet, I would place a 

 pointed bar six feet long, inclining outward at an angle of 45° ; 

 all these bars should be connected at their bases by a 

 broad strip of sheet copper led along the wall. 



I have the honor to be, Sir, 



Your most obedient servant, 



W. B. OShaughnessy, M. D. 



Assist. Surgeon and Prof. Med. Col. Calcutta. 

 Medical College, 22d June, 1840. 



