LIGHTNING 



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LIGHTNING 



tery and the danger of lightning and thunder; 

 they believed that these were weapons in the 

 hands of Zeus, or Jupiter. So powerful and 

 so deadly were these weapons that they could 

 belong only to Jupiter, greatest of the gods. 

 Modern science has removed much of the mys- 

 tery surrounding lightning, and has proved that 

 lightning is really atmospheric electricity. 



It was Benjamin Franklin who first showed 

 the identity of electricity and lightning. He- 

 made a silk kite, near the top of which he 

 fastened a piece of wire. He next attached a 

 long string to the kite, tied an iron key to the 

 free end of the string and fastened a silk rib- 

 bon to the key. Silk is not a conductor of 

 electricity. One day in a heavy thunderstorm 

 he sent up the kite. The first thundercloud 

 passed without any apparent effect, but as a 

 second one came near the kite he saw that 

 the loose ends of the string stiffened. He put 

 his hand near the key and instantly felt a 

 shock as a tiny spark bridged the space from 

 the key to his finger. Rain then fell heavily 

 and the wet kite string carried so heavy a cur- 

 rent of electricity that Franklin charged a Ley- 

 den jar (which see). 



What Causes Lightning? Franklin first 

 proved that lightning is electricity, and then 

 showed by experiments that the electricity, in 

 the clouds is both positive and negative, ex- 

 actly as some bodies on earth, when electrified, 

 produce positive or negative electricity. The 

 earth's surface as a whole is charged with nega- 

 tive electricity, whereas most of the clouds 

 are charged with positive. The difference be- 

 tween these two kinds of electricity is chiefly 

 a difference in condition rather than in nature, 

 as explained in the article ELECTRICITY. 



The important point to remember is that 

 positive and negative charges of electricity 

 mutually attract each other. Nobody knows 

 why this is true; scientists have merely learned 

 it by experiment. The air, however, is a non- 

 conductor, that is, it does not hold electricity, 

 and as the winds blow the clouds here and 

 there the different charges of electricity seek 

 a weak spot in the wall of air separating them. 

 When this weak spot is found the electricity 

 jumps across the space with a flash which is 

 called lightning. A flash of lightning is ex- 

 actly like a spark from a Ley den jar or from 

 any other charged body. 



Perhaps the lightning flash will be more 

 easily understood by comparison with water. 

 Let the reader imagine that a dam is placed 

 in such a way that it prevents two rivers from 



making a junction; then imagine the shower 

 of spray which will rise when the dam sud- 

 denly breaks. When two clouds, or the earth 

 and a cloud, get so close together that there 

 is an electrical discharge, there is a shower of 

 sparks. Very few people realize that a flash 

 of lightning is really a succession or shower of 

 flashes so close together that they seem like 

 one to the naked eye. 



All electrical discharges are alternating, that 

 is, every spark is followed by a pause. These 

 intervals between sparks vary from a few 

 thousandths to a few millionths of a second 





POSITIVE AND NEGATIVE ELECTRICITY 

 Lightning 1 is an electric discharge between two 



clouds, one electrified positively and the other 



negatively, or between a cloud and the earth. 



Positive electrification is indicated above by the 



sign + ; negative, by the sign . 



in length. Lightning is a discharge of elec- 

 tricity from countless millions of electrified 

 particles in the clouds or on the earth, and a 

 flash is made up of these countless sparks 

 which all occur at the same time. This mix- 

 ture of sparks and pauses causes the flickering 

 or vibrating appearance which is frequently 

 noticed in lightning. 



Why Are Clouds Charged with Electricity? 

 While it is clear that lightning is caused by 

 electricity in the clouds, yet the question 

 arises, "Why are clouds charged with elec- 

 tricity?" Nobody has yet explained to every- 

 body's satisfaction what electricity itself is, 

 and nobody has yet proved why it is found in 

 the clouds. Scientists have said that it is due 

 to friction in the air caused by floating par- 

 ticles of dust, or to friction caused by snow- 

 flakes and particles of water in the upper 

 layers of clouds. It has also been suggested 

 that it is in some way the result of the evapora- 



