Lightning Conductors. 11 



building will require more projecting points than a tall one 

 like a church with a spire. 



Materials. — Any metal can be used, but lead and zinc 

 being worse conductors than copper and iron, a larger sur- 

 face of the former than the latter would be necessary. The 

 form may be in rod wire, sheet, or tube, as most convenient. 

 No less surface than is presented by wire quarter of inch 

 thick should be used for copper or iron, and at least ten 

 times that for zinc or lead. 



Lead or metal ridging and guttering may be used if 

 soldered at the joints ; but as it is not safe to solder 

 the laps themselves, as they would tear by expansion 

 and contraction, a method similar to that suggested in the 

 report of the French Academy for connecting iron frame- 

 work in lightning conductors should be adopted, namely, 

 at each joint a strip of copper to form a bridge over it, 

 should be soldered, so that the bridge of metal will always 

 give and take in the sliding of the lap due to expansion 

 and contraction. 



Down-pipes for conveying rain-water from the roof may 

 also be used, if a similar device with regard to joints be 

 adopted, and if a good plan for metallically connecting the 

 guttering with the head of the pipe, and the foot of the 

 pipe with the earth, be devised. 



In most modern buildings the metal used on the roofs can 

 be made to form a very effective portion of the system of 

 a lightning conductor, by keeping in mind the foregoing 

 suggestions, and all the ridging, guttering, &c, will in reality 

 form a portion of a metallic cage protecting the roof. 



Whether such metallic parts of the building form part of 

 the true conductor or not, it will always be safest to connect 

 all those parts together and with the conductor. 



To put the foregoing into a more practical form, let the 

 case of a church, with a spire 120 feet high, and a roof 100 

 feet long, be taken ; the spire may have a terminal and 

 weather vane of iron, or of wood sheathed in copper ; then 

 from the terminal below the vane, a copper or iron rod 

 should spring to a little above the vane, terminating in the 

 gilded copper point as already described; then from the 

 base of the pinnacle, well soldered copper or iron rod, 

 strip, tube or rope, take it down outside the spire to the 

 metal rido-e of the roof, to which it should be soldered in 

 passing ; carry it down to the earth, connecting by solder 

 any metal guttering that it may come near on the way, and 



