-1859] WRITINGS OP JOSEPH HENRY. 401 



may be insulated by cylinders of glass. We do not think 

 the latter however of much importance since they soon be- 

 come wet by water, and in case of a heavy discharge are 

 burst asunder. 



7th. The rod should be connected with the earth in the 

 most perfect manner possible, and in cities nothing is better 

 for this purpose than to unite it in good metallic contact 

 with the gas mains or large water pipes in the streets ; and 

 such a connection is absolutely necessary if the gas or water 

 pipes are in use within the house. This connection can be 

 made by soldering to the end of the rod a strip of copper, 

 which, after being wrapped several times around the pipe, 

 is permanently attached to it. Where a connection with the 

 ground cannot be formed in this way the rod should termi- 

 nate, if possible, in a well always containing water, and where 

 this arrangement is not practicable it should terminate in a 

 plate of iron or some other metal buried in the moist ground. 

 Before it descends into the earth, it should be bent so as to 

 pass off nearly perpendicular to the side of the house, and it 

 should be buried in a trench, surrounded with powdered 

 charcoal. 



8th. The rod should be placed, in preference, on the west 

 side of the house, in this latitude, and especially on the 

 chimney from which a current of heated air ascends during 

 the summer season. 



9th. In case of a small house a single rod may suffice, 

 provided its point be sufficiently high above the roof, the 

 rule being observed that its elevation should be at least half 

 of the distance to which its protection is expected to extend. 

 It is safer however, particularly in modern houses in which 

 a large amount of iron enters into the construction, to make 

 the distance between two rods less than this rule would in- 

 dicate rather than more. Indeed we see no objection to an 

 indefinite multiplication of rods to a house, provided they 

 are all properly connected with the ground and with each 

 other. A building entirely enclosed, as it were, in a case of 

 iron rods so connected with the earth would be safe from the 

 direct action of the lightning. 



10th. When a house is covered by a metallic roof the latter 



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