LIGHTNING CONDUCTOR. 



Fig. 2. 



follows bell- wires, metallic mouldings of walls and furniture, and 

 fuses gilding. 



21. The purpose of paratonnerres or conductors, erected for the 

 protection of buildings, is not to repel, but 

 rather to attract lightning, and divert it into 

 a course in which it will be innoxious. 



A paratonnerre is a pointed metallic rod, 

 the length of which varies with the building 

 on which it is placed, but which is generally 

 from thirty to forty feet. It is erected ver- 

 tically over the object it is intended to pro- 

 tect. From its base an unbroken series of 

 metallic bars, soldered or welded together 

 end to end, are continued to the ground, 

 where they are buried in moist soil, or, 

 better still, immersed in water, so as to faci- 

 litate the escape of the fluid which descends 

 upon them. If water, or moist soil, cannot be 

 conveniently found, it should be connected 

 with a sheet of metal of considerable super- 

 ficial magnitude, buried in a pit filled with 

 pounded charcoal, or, better still, with braise. 



The parts of a well-constructed paratonnerre 

 are represented in fig. 2. The rod, which is of 

 iron, is round at its base, then square, and 

 decreases gradually in thickness to the summit. 

 It is composed commonly of three pieces closely 

 jointed together, and secured by pins passed 

 transversely through them. In the figure are 

 represented only the two extremities of the 

 lowest, and those of the intermediate piece, to 

 avoid giving inconvenient magnitude to the 

 diagram. The superior piece, g y is represented 

 complete. It is a rod of brass or copper, 

 about two feet in length, terminating in a 

 platinum point about three inches long, at- 

 tached to the rod by silver solder, which is 

 further secured by a brass ferule, which gives 

 the projecting appearance in the diagram below 

 the point. 



Three of the methods, reputed the most 

 efficient for attaching the paratonnerre to the 

 roof, are represented in fig. 3, at p, I, and f. 

 At p the rod is supported against a vertical piece, to which it 

 is attached by stirrups ; at I it is bolted upon a diagonal brace ; 



185 



