ATMOSPHERIC ELECTRICITY. 395 



ing, as gutters, pipes, etc., they should be connected with 

 the rod by strips of metal, and directly, if possible, with 

 the ground. The lower end of the rod, where it enters 

 the ground, should be divided into two or three branches, 

 and turned from the building. 



It ought also to extend so far below the surface of the ground as to reach 

 water, or earth that is permanently damp. It is, moreover, a good plan to 

 bury the end of the lightuing-rod in powdered charcoal, since this pre- 

 serves in a measure the iron from rust, and facilitates the passage of the 

 electricity. 



A building will be most perfectly protected when the lightning-conductor 

 has several branches, with pointed rods projecting freely in the air from dis- 

 tant summits of the building, and connected with the main rod. 



Professor Faraday advises that Ughtning-conductors should be arranged 

 upon the inside of buildings rather than upon the outside. 



wiiat space -^ lightning-conductor of sufficient size is 

 rjdprlftectf""' believed to protect a circle the diameter of 

 which is four times the length of that part of 

 the rod which rises above the building. Thus, if the rod 

 rises two feet above the house, it will protect the building 

 for (at least) eight feet all round. 



A lightning-conductor m.ay be productive of harm in two 

 W lien may a - j r .n-j 



lightning-rod ways ; if the rod be broken or disconnected, the electric fluid, 



''f ha"^*'''?*'''''^^ being obstructed in its passage, may enter the building; and 

 if the rod be not large enough to conduct the whole current 

 to the earth, the lightning will fuse the metal and enter the building. 



A lightning-conductor protects a building even when no visible discharge 

 takes place, by attracting the electricity of an approaching cloud, and caus- 

 ing it to pass off silently and quietly into the earth. This process commences 

 as soon as the cloud has approached a position virtically over the rod. 



7G8. As regards safety in a thunder-storm, it is prudent, if 

 are safe and out of doors, to avoid trees and elevated objects of every 



what danger- j^j^^j ^\^{q\.^ ^\^q hghtning would be likely to strike in its pas- 

 ous in a thun- ) o o j f 



der-stormf sago to the earth. A stream of water, being a good conduc- 



ductor, should be avoided. 

 If witliin doors, the middle of a carpeted room is tolerably safe, provided 

 there is no lamp hanging from the ceiling. It is prudent to avoid the neigh- 

 borhood of chimneys, because lightning may enter the room by them, soot 

 being a good conductor. For the same reason, a person should remove a3 

 far as possible from metals, mirrors, and gilt articles. The safest position that 

 can be occupied is to he upon a bed in the middle of a room — feathers and 

 hair being excellent non-conductors. In all cases, the position of safety is 

 that in which the body can not assist as a conductor to the hghtning. Tho 



