284: SCIENCE OF COMMON THINGS. 



Lightning conductors. Their proper principle of construction. 



are proportionate to the magnitude of the evils it pro- 

 duces, rather than the frequency of its occurrence. The 

 chances of an individual being killed by lightning are 

 infinitely less than those which he encounters in his 

 daily .walks, in his occupation, or even during his sleep 

 from the destruction of the house in which he lodges 

 by fire. 



185S Why does the lightning in its course down a building generally 

 dart from point to point, and not follow a direct path ? 



Because it always takes in its course the best conduc- 

 tors ; and will fly both right and left in order to reach 

 them. 



1853 What is a lightning conductor f 



A metal rod fixed in the earth, running up the whole 

 height of a building, and rising in a point above it. 



185<b What metal is best, for this purpose f 



Copper makes the best conductor. 



1855 What is the use of a lightning conductor f 



As metal is a most excellent conductor, lightning 

 (which makes choice of the best conductors) will run 

 down a metal rod rather than the walls of the building. 



1856 Why should lightning conductors be pointed f 



Because points conduct electricity away silently and 

 imperceptibly. 



Blades of grass, ears of corn, and other pointed objects serve to with- 

 draw electricity from the clouds. 



1857* How far will the beneficial influence of a lightning conductor 

 extend f 



It will protect a space all round four times the length 

 of that part of the rod which rises above the building. 



1858 Give me an example. 



If the rod rises two feet above the house, it will pro- 

 tect the building for (at least) eight feet all round. 



1859 How can lightning conductors be productive of harm ? 



If the rod be broken, the electric fluid (being obstruct- 

 ed in its path) will enter the building. 



18BO Is there any other evil to be apprehended from a lightning rod f 



Yes ; if the rod be not large enough to conduct the 



