1840.] On Lightning Conductors to Powder Magazines. 291 



11. There can be no doubt, that a conductor in the moment 

 of a discharge of electricity passing through it, influences in a 

 degree, all good conducting substances in its immediate vicinity 

 by induction; but no discharge will take place from it to any 

 neighbouring body, unless it be insufficient itself to conduct the 

 whole of the discharge \ or unless the body in its vicinity be a 

 better conductor than itself. A lateral discharge, in fact, is only 

 a division of a portion of the principal discharge, from an 

 insufficient conductor to another, which can relieve it. Now 

 the very purpose of a lightning rod is to provide a suffi- 

 cient conductor for the electric fluid which may fall upon it, 

 and which will never pass from it, if properly constructed, 

 to any building in its immediate vicinity, from the construc- 

 tion of which all metallic substances are, of course, carefully 

 excluded. 



12. Thirdly, Dr. O'Shaughnessy refers to Dr. Goodeve's 

 house having been struck by lightning, within twenty feet of a 

 well constructed conductor upon the house of Mr. Trower, which 

 was struck at the same moment, as falsifying the opinion that 

 within sixty feet interval between conductors no accident can 

 occur ; but in another part of his report he attributes this acci- 

 dent, doubtless very correctly, to the vertical window bolts, 

 which he has marked upon his plan, and which constitute a line 

 of interrupted conductors to the ground. There can be no 

 question that the discharge was diverted in this instance ; but 

 it does not appear that any damage was done to either house ; 

 and if damage did occur to the unprotected house, it would have 

 been doubtless greatly increased by the absence of the conduc- 

 tor upon Mr. Trowels house. 



It would of course be an act of the greatest folly and igno- 

 rance to place a similar line of bolts, or any other metallic fasten- 

 ing upon a powder magazine. 



13. The case by no means proves, as Dr. O^Shaughnessy seems 

 to think, u that occasionally, in tropical climates, there is such a 

 vast disproportion between the intensity and quantity of the 

 atmospheric electricity, and the conducting capacity of protec- 

 tors, that the excess of the discharge must pass to adjacent 



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