BOOK III. CHAP. VII. ,641 



from the wall, and then bent again downwards tlirec or four feet, 

 it will prevent any damage to the ftones of the. foundation. 



For the upper part, Mr. Franklin propofes, that it fliould be raife'd 

 fix or eight feet above the higheft part of the building ; and that 

 it (hould be tapered gradually to a {\vii:JImrp point, and the point gilt, 

 to prevent its rufting. — But a diftcrence of opinion has arifen concern- 

 ing the uie of po'nitcd rods, inftead of hlunt, or unpointed. 



Mr. Franklin's fyftem is, " X.\\-M points have an equal power to throw 

 " off, as to draw on, the ele£lric fire." — " '^V\^■^iX. points attradl ele6lricity 

 " at greater diftances in the gradual filent way ; but that, knobs will 

 " attradt a ftroke at the greateji diftancc." — " That ponts tend to re- 

 " pel the fragments of an electrified cloud ; but that, knobs dxdiW xX'^iW 

 " nearer." 



To thefc pofitions Mr. Wilfon has obje^^ed very fubftantial reafons. 



That it does not appear that po'ints draw off and condu£l away 

 lightning imperceptibly, without explofion, during a thunder ftorm ; 

 but, on the contrary, there are many inftances, where violent explo- 

 fions of lightning have happened to conduftors that were Jlmrply 

 pointed., and three in particular, the account of which was given in 

 Mr. Franklin's publication ; where \\\t points were diflipated or de- 

 ftroyed, and a fmall part of an iron rod melted at the place of the 

 point's infertion. — That every point is to be conlidered ^% Joliciting the 

 lightning, and, by that means, not only contributing to increaje the 

 quantity of every adiual difcharge ; but alfo frequently occafioning 

 a difcharge, where it might not otherwife have happened. If, there- 

 fore, we invite the lightning, whilft we are ignorant of what the 

 quantity or the efFe£ts of it may be, we may be promoting the very 

 mifchief we mean to prevent. Whereas if, inftead of pointed, we 

 make ufe of blunted condu6lors, thofe will as effeftually anfwer the 

 purpofe of conveying away the lightning flifely, without that ten- 

 dency to increafe or invite it. — Points are meant to invite or draw 

 off the lightning continually ; but we find, from experience, that 

 they are extremely fubje6l from their tenuity to be melted down, and 

 deftroyed ; they are, therefore, fo far rendered ufelefs and vain, as no 

 one can exailly fay what the duration, or what the effedts, of any 

 florm of lightning may be ; and many difficulties may occur in the 

 timely replacing of fuch as are fo melted, or rendered ufelefs. Light- 

 ning ads with more power upon Jlmrp points, than blunted ends, in 

 the proportion of at leafl 12 to i. And as blunted conduftors, of fuf- 

 ficient dimenfions, are found capable of conveying away the light- 

 ning fafely whenever it attacks them, why fhould we have recourfe 

 to a method which is uncertain, and may be dangerous ? 



Vol. III. 4 N A for- 



