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



22. But as it may be deemed inexpedient to commit a ma- 

 gazine even to the chances of an equal area of land surface,, I 

 think a system of conductors on the following plan would pre- 

 vent all danger of explosion by direct, or lateral, or even return 

 discharge. 



I would erect an iron rod, half an inch in diameter, protect- 

 ed by zinc, at every twenty paces, in a circle drawn round the 

 building, and at least twenty feet* distant from it. These rods 

 should be twenty feet higher than the building, be supported 

 by frames of wood or by pillars inserted at their bases, as 

 deep as the water level (so easily found in Bengal), and at 

 the surface of the ground they should be connected by ho- 

 rizontal rods secured by riveting. During storms the sen- 

 tinels on duty should withdraw beyond this line, sheath their 

 bayonets, and pile their arms. 



I cannot conceive the possibility of an explosion caused by 

 direct, lateral, or return discharge, taking place within this 

 metallic circle. By such arrangements it is that the electrician 

 discharges through a wire bird cage, without injury to its tenant, 

 batteries sufficiently powerful to destroy a horse, and that he 

 grasps the discharging rod in his naked hand while it is part 

 of a circuit sufficient to cause his instantaneous death. 



I have the honor to be, Sir, 

 Your obedient servant, 

 Medical College, Calcutta, W. B. O'ShauGHNESSY, 



27th Dec. 1838. Assistant Surgeon, 



(No. 3.J 



To W. B. O'Shaughnessy, Esq. M. D. 



Medical College. 



Ordnance Department. 



Sir, — I am directed by the Military Board to acknowledge 

 the receipt of your letter of the 31st ultimo, on the subject of 

 Lightning Conductors to Powder Magazines; and to express 

 the sense which the Board entertains of the care and attention 

 with which the subject has been discussed. 



* This by an error of the copyist was made paces in the MS. report. — 

 W. B. O'S, 





