3U 



THE FARMERY. 



[ClIAP. III. 



from lightniiig, because their coiuluctiiig power varies so miicli, and very 

 often, when in their best conchieting condition, they are damaged by tlie 

 lightning passing over them. The conducting power of shade-trees, then, 

 slionld be increased and made permanent by the application of an iron or 

 copper •wire. 



" Ekkoes. — One of the errors committed in protecting from lightning is 

 an improper estimate placed upon tiie conducting power of the building, 

 compared with the material used for protection. "When a lightning-con- 

 ductor terminates or ends iu a substance of imperfect or less conducting 

 power, it is reduced to the conducting power of the body iu which it ends. 



" Dry earth is a non or imperfect conductor. Earth owes its conducting 

 power to water. According to Cavendish, the conducting power of iron, as 

 compared to the conducting power of water, is as four hundred millions to 

 one. The electrical size of the mass of lightning-rods is not as large as a 

 common knitting-needle, being reduced by so small a portion of the rod's 

 surface coming in contact with damp earth. 



"Another error is in constructing the rod in sections. Rods properly 

 applied, of jDerfect continuity, being all in one piece, without coupling or 

 hooking, have never failed to carry the quantity of electricity that may 

 have passed iijion them safely and successfully to the ground, while the sec- 

 tioned, or the rods hooked or screwed together by burs or nuts, have fre- 

 quently failed to do their duty. Scarcely a day or a week passes during 

 the summer months but we hear of the failure of the couj^lcd lightning-rods. 



" However well the fact of electrical conduction may be known — however 

 well scientific men may be agreed that by the judicious employment of 

 metallic bodies we may increase protection against lightning, certain it is 

 that tiiey have taken too much upon trust, and neglected the investigation 

 of the facts. 



" Men ignorant of every electrical principle have professed to furnish 

 security against lightning, until the scientific electrician who attempts to 

 sell lightning-rods is received M-ith jeers and contempt as a designing 

 swindler ; his story is listened to with impatience, and his presence consid- 

 ered an intrusion." 



The rod recommended by Mr. Cushman is made of four copper and four 

 iron wires laid together, with a pointed cap on the top, and some metal plates 

 at tiie bottom. There must never be a splice in the wire, but several wires 

 carried up from the ground, in the main body, may be taken off and con- 

 nected with the metal roof of a building, or with other points. 



The following language we used upon a discussion of this subject before 

 the American Institute Farmers' Club : 



"As lightning-rods are most commonly constructed, they are not what 

 they arc generally conceived to be — that is, attractoi's of an approaching 

 thunderbolt, picking it up on the sharp points, and conducting it down a 

 carefully insulated rod to a safe deposit iu the earth. If a lightning-rod 

 ever performed such a service, I should like to be assured of the fact. At 



