No. 3. 



0)1 Lii^htning Rods. 



75 



fir:nor strikin^r ilistmico. As t'lo ball n\)- 

 jpro.inhe-s no spnrk will be perceived; tlic 

 point entirely prevents the. str.thr. 



4. That when Iho bail mul point are both 

 presented to tiio cli^ctrified Uxiy, but with 

 the point much lartlier off than the ball, the 

 point will still dischari^e the electricity of (he 

 body before the ball arrives within strikinir 

 distance, and the stroke will be prevent' d. 

 This experiment shows that the point ope- 

 rates on the charged body at a much greater 

 distance than the ball. — Fijr. 14. 



Fig. H. 



The phenomena mentioned in the last para- 

 graph, occur with uniform regularity whether 

 we employ an amber bead, e.xciteil by fric- 

 tion, — an electrical machine, — or the p-nble 

 mantle of the skies, as it hurls "the dread 

 artillery of heaven" on a devoted world. 

 They result from the nature of the electric 

 fluid, and are in strict obedience to determi- 

 nate laws by which it is governed. They 

 are precisely the same, whether brought into 

 play by drawing a silk stocking; by strokinof 

 tlie b.ick of a cat; by working an electrical 

 machine; or by the more grand and terrific 

 movements of a thunder cloud. Wherever 

 electricity occurs, it is subject to the same 

 laws. A ball will always receive it in form 

 of an explosive spark when brought within 

 strikins; distance ; a point will as certainly 

 draw it off in a silent invisible stream, at 

 several times the distance which the charge 

 is cnpihle of striking to — when both are 

 used, the point will entirely prevent the 

 stroke. 



Having ascertained these simple f;\cts, and 

 referred them to their governing laws, it be- 

 came an easy task for the keen perceptions of 

 a Franklin, to discover how they might be ap- 

 plied to protect buildings ngiinst lightning. 

 He compared the electrified body to the thun- 

 der cloud; thi^ ball to the building, and the 

 poi7it to the lightning rod, see fig. 15, and 

 the parallel was complete. The two arrange- 

 mentfi were composed of the same parts ; they 



were nece-^.^arily smijecL lu iiit,- o^aic jjovcrn- 

 ing laws, and the result in the two cases 

 um.-t lie the same. Thus he arrived at the im- 

 portant conclusion, that t/ir rod wi.l draw off 



Fi.e, 1.5 

 Ihe eh'rtricihj from the cloud before it comes 

 near enough to strike to the building. It 

 was tliis inductive rea.soning from scientific 

 truths which 



" Bade his bold arm invade the lowering sky, 

 Ai,d sieze the tiptoe hghtnings ore they fly." 



To render the subject still more clear, .sup- 

 pose the clond, in tiie last figure, to be capa- 

 ble of sirikinij the house at the di.stance of 

 ten yirds; but it has been shown that the 

 p(jint will operate at several times the strik- 

 ing distance, say tliirty yards; it must, there- 

 fore, f<)llow that the point would remove all 

 danger from the cloud before it came near 

 enough to strike the building. The reader 

 must bear in mind, that these numbers are 

 not set down as the actual distances at which 

 the ball and point will operate. No such 

 distances can be assigned, because they con- 

 tinually vary from nothing up to an indeter- 

 minate extent, as the intensity of the electric 

 charge and other circumstances vary. 



It is hoped that this brief exposition of the 

 principles of electrical science, will dispel 

 the doubts of some ; inspire others with con- 

 fidence in the protective influence of light- 

 ning rods; and prepare all to comprehend the 

 fl)llowing directions fiir their construction. 

 The amount of protection which they afl^ord, 

 depends upon this. If improperly made, they 

 mav even prove a dangerous appendage to a 

 buildiuL'. The following particulars should 

 be carefully attended to. 



The body of the rod mav, very conve- 

 niently, be made of five-eighths or three 

 quarters bars of round or rolled iron. If 

 practicable, the bars should all be welded into 

 one piece. Where this cannot be done, a 

 deej) socket should be formed in the lower 

 end of the upper piece, so as to fit accurately 

 on the top of the lower one. The incumbent 

 weight will then keep the parts in complete 

 contact. The lower end of tlie rod, to a short 



