LIGHTNING 



3429 



LIGHTNING 



HOW TO AVOID BEING STRUCK BY LIGHTNING 



(A) Distance from storm. It takes five seconds for the noise of thunder to travel one mile; (1) 

 is two and a half seconds, or half a mile, and is safe for the time being; (2) is the safe distance of 

 a mile, and (3) is two miles.. 



(B) If caught on open grovuid, lie flat. It is dangerous to stand or run. 



(C) Treat a person who has been struck by lightning in the same way as one who has been nearly 

 drowned (see DROWNING). 



(D) In a thunderstorm avoid placing yourself between two conductors such as a gas main (4) 

 and the fireplace. 



tion of water from the surface of oceans, lakes 

 and streams, but this theory has not won 

 much support. A more probable explanation 

 is that electricity in the air is due to the con- 

 stant bombardment of the outer layers of air 

 by hosts of electrified particles, called electrons, 

 issuing with enormous velocity from the sun. 

 Kinds of Lightning. There are three recog- 

 nized forms of lightning, the first of which is 

 called forked, zigzag or chain lightning. This 

 is a line of brilliant light; it usually appears 

 zigzag to the eye, but in fact is winding like 

 a river. The single streak often breaks into 

 several branches or forks. The second kind is 

 called sheet lightning. This has no particular 

 form, but is usually a bright flash which spreads 

 uniformly over the horizon and lights up the 

 skies. Sheet lightning is really the illumina- 

 tion in the sky due to zigzag or chain lightning 

 which is itself beyond the horizon or is for 

 some other reason invisible to the eye. Heat 

 lightning, frequently seen on summer evenings, 

 is practically the same as sheet lightning. The 



third form of lightning is called ball lightning. 

 Balls of fire, a foot or two in diameter, descend 

 slowly from the clouds, until they strike the 

 earth; sometimes they even roll along over the 

 ground. The ball explodes when it hits the 

 ground or some obstacle, but it does not seem 

 to be very dangerous. Ball lightning is the 

 least understood of all forms, and it is only in 

 recent years that scientists have begun to in- 

 vestigate it; previously it was classed with the 

 sea serpent and other semimythical wonders. 



Why Thunder Follows Lightning. The elec- 

 tric discharge, as it breaks its way through the 

 atmosphere, instantaneously heats the air in 

 its path. This sudden heating causes a vio- 

 lent expansion of the air along the path of 

 the lightning flash, and a violent compression 

 of the cool air farther away. This process 

 starts a great air wave which is the thunder. 

 When a lightning flash occurs near by, the 

 sharp, crackling reports come from its branches, 

 and the heavy crash comes from the trunk of 

 the flash. The rolling thunder comes from 



