.640 J A M A I • C -A. 



iiig from one to the other, if not far diilant from cacli other, oiilj 

 r-ending the wall in the fpaces wliere thefe partiah good conductors 

 are too diftant from each other. ^- An iron rod being placed on the 

 . outfideof a building, following the form of the roof or other parts, 

 and continued from the highelt paits down to the moift earth in any 

 - direction, rtrait or crooked, v/ill receive the lightning at its upper 

 end, attracting it lo as to prevent its ftriking any other part; and af- 

 fording a good conveyance into the earth, will hinder it from da- 

 maging any part of the building. A fmall quantity of metalis found 

 . able to conduct a great qujntity of this fluid. Wire no bigger than 

 a goofe-quill, has been known to conduct (with fafety to the build- 

 ing as far as the wire was continued) a quantity of lightning that did 

 prodigious damage, both above and below it; in North America, it is 

 common to make it of half an inch, fome of three quarters, or an inch 

 diameter. — Mr. Wilfon is of opinion, that the conductors fliould be made 

 of one piece of metal otily, and of an equal diameter throughout. What 

 this diameter ought to be, may depend on the magnitude of the build- 

 ing to be protedted ; but, 'fince no one can fix the limits of the greateft 

 difcharge that may poffibly happen, it is fafejl to uie conductors, or 

 rods, of fuch thicknefs as to promife fecurity againfl: the nioft vio- 

 lent attacks ; therefore, ^ gooje-qu'ill ivlre is certainly not fo fafe as one 

 of larger dimcnlions; and, in confirmation of this, we are told of a 

 bar of iron of one inch diameter, erefted in Martinico, which, by a 

 violent ftroke of lightning, was reduced in one part to the thicknefs 

 only of a Qender wire°. A rod therefore of i \ inch diameter, or 

 even 2 inches, will not be too large. — Chains arc improper, as well 

 as pieces of metal linked together, becaufe the links though appa- 

 I'-ently in contaft with each otlier, are not abfolutely fo, but are di- 

 vided by fpaces imperceptible to the eye ; and the lightning, in en- 

 deavouring to pafs from one link to another, frequently melts them 

 by its violent adtion, whilfl: the other parts remain entire. — The rod 

 may be fafiened to the wall, chimney, ^c. with Itaples of iron. 

 The lightning will not leave the rod (a good condu6tor) to pafs into 

 the wall (a bad conduftor) through the flaples ; it would rather, if 

 were in the wall, pafs out of it into the rod to get more readily by that 

 conductor into the earth. — If the building be very large and extenfive, 

 two or more rods may be placed at difFeient parts, for greater fecurity. 

 — The lower end of the rod fhould enter the eartli fo deep, as to 

 come at the moilt part, perhaps two or three feet; and if bent when 

 under the lurfacc, lb as to lie in a horizontal line fix or eight feet 



° I fufiicil: lliciru'as a drolTineP:, or feme ntlicr dclcvl in tlic fuhfl.incc of the bar, at (hit part of 

 it, which ciiulld an inteintption to tlic ircc ciurcrt of the ilciftric ttreani through it. 



I from 



