460 



THE POPULAR SCIENCE MONTHLY 



" Think now," says Lodge, "of a cloud and of the earth under 

 it as forming the two coats of a Leyden jar, in the dielectric of 



which houses and people exist ; we now 

 have to consider what determines a dis- 

 charge, and what happens when a dis- 

 charge occurs. The maximum tension 

 which air can stand is one half gramme 

 weight per square centimetre. At what- 

 ever point the electric tension rises to this 

 value, smash goes the air. The breakage 

 need not amount to a flash, it must give 

 way along a great length to cause a flash ; 

 if the break is only local, nothing more 

 than a brush or fizz need be seen. But 

 I when a flash does occur it must be the 

 x weakest spot which gives way first — the 



1 place of maximum tension — and this is 

 < commonly on the smallest knob or surface 

 - which rears itself into the space between 

 & the dielectrics. If there be a number of 



O 



3 small knobs or points, the glows and brushes 



g become so numerous that the tension is 



g greatly relieved and the whole of a mod- 



^ erate thunder-cloud might be discharged 



2 in this way without the least violence. . . . 

 S But sometimes a flash will descend so quick - 

 w ly or it will have such a tremendous store 

 % of energy to get rid of that no points are 

 I sufficiently rapid for the work, and crash it 

 "■ all comes at once. One specially note- 

 « worthy case is when one cloud sparks into 



^ ° another and thence to the ground; or in 

 _ ^ general whenever electric strain is thrown 



b^ quite suddenly upon a layer of air/' 



"^ ^ Thus, then, we begin to see that much. 



^ 5 will depend upon the character of the flash. 



I ' There are many flashes, I believe, that the 



^ body could experience without very seri- 



al ous consequences ; and there are many 



S that will rive solid granite and shatter in 



I splinters the heaviest masonry. The im- 



^ pulsive rush discharge shown on the pre- 



ceding page was doubtless a flash of the 

 latter character; and on the other hand, 

 with a kite in air during thunderstorms with a wire connection 

 to the ground I have experienced sharp shocks with lightning 



