28(5 SCIENCE OF COMMON THINGS. 



Utility of lightning-rods. What is thunder ? 



1867 How should the lower end of the rod be arranged ? 



It should be divided into two or three branches, and 

 turned from the building. 



The end of the rod ought to extend so far below the surface of the 

 ground as to reach earth that is permanently damp. 



1868 Why is it a good plan to bury the end of the rod in powdered 

 charcoal f 



Because it preserves the iron from rust, and facili- 

 tates the passage of the electricity. 



1869 Have we any proof of the utility of lightning rods f 



The experience of a hundred years has shown that 

 when all the necessary rules have been observed, the 

 protection is perfect, as far as human effort can avail. 



187*0 Is a buikling more or less liable to be struck when furnished with 

 a good lightning conductor f 



Lightning conductors do not, as many suppose, attract 

 the lightning towards the building on which they are 

 situated ; they simply direct its course, and facilitate 

 the passage of the fluid in the most direct way to the 

 earth, only when a discharge must inevitably occur. 

 There is no attraction, but the lightning takes the road 

 which offers the least resistance. 



187*1 Are lightning conductors protective when even no visible discharge 

 takes place f 



They are; they possess a very great preventive 

 power, and gradually and silently disarm the clouds by 

 conducting the electricity from them ; and this process 

 commences as soon as the cloud has approached a posi- 

 tion vertically over the rod. 



18 7S What is thunder? 



It is a certain noise proceeding apparently from the 

 clouds, which usually follows, after a greater or less 

 interval, the appearance of a flash of lightning. 



187*3 How is it supposed to be occasioned? 



The usual explanation offered is a sudden displace- 

 ment of the air produced by the electrical discharges in 

 which the lightning is evolved. 



Others have supposed that the passage of the electric current creates a 



