38 



Introduction to the Study of Science 



The electrical display and the majestic roar of thunder are 

 interesting features. It is possible here to mention briefly 

 only a few of the important conditions upon which electric 

 discharge or lightning depends ; and these are given primarily 

 to stimulate further observation and study of such phenomena. 





Fio. 12. Vertical section of a thunder storm, showing the vertical whirl. 

 A whirl parallel to the ground would be a whirlwind, tornado or waterspout. 

 (After Arrhenius.) 



Exercise : Electrical discharge. If the school has an electrical 

 machine, such as the Wimshurst, and condensers or Leyden jars, the 

 essential features of electrical discharge may be illustrated. Try 

 making sparks pass through different distances and media, as wet and 

 dry paper. If the charge is great and the distance rather long-, forked 

 sparks may be produced. Zigzag paths are easily illustrated. The 

 sound by the sparks may be considered as thunder. 



Electrification of the air. The air that lies nearest the earth 

 is practically devoid of electrical energy ; but the layers above 



