922 TjiAySACTIOiXS OF THE AMERICAN LxSTHUlE. 



purtic'les of ice in the atmosphere may, under certain circumstances, 

 become luminous. 



The electrometer sometimes detects negative electricity in cloud 

 and in rain, snow and hail ; hut M. Palmier and others now think that 

 this is only an effect of induction, and that no cloud can be intrin- 

 sically negative. 



Every positively charged cloud must have a concentric region about 

 it, which is made negative by induction, and it has happened that 

 persons have been killed by lightning, or rather by what is called 

 return shocks in a clear atmosphere, in consequence of such induction. 



This is a phenomenon, easily explained. 



When a storm cloud is powerfully electrified positively, and a 

 person is situated within its sphere of activity, he becomes powerfully 

 charged by induction with negative electricity, the natural electri- 

 city of the person being decomposed and the positive repelled into 

 the earth. 



iN'ow, if the cloud is suddenly discharged by any means, and 

 deprived of a large portion of its positive electricity, the natural 

 electricity of the person is just as suddenly restored, and the shock 

 may be such on the nervous system as to destroy life. 



Brydon has related a remarkable case of this kind, in which a man 

 named Lauder, who was driving a coal cart, was killed, together with 

 his horses, where the sun was shining and no rain was falling in the 

 neighborhood ; but a heavy clap w'as heard at the time by others, 

 from a cloud not far distant. 



Beside this phenomenon of retiirn sliock^ there are lightnings of 

 three distinct kinds : 



FiKST. — Zigzag oe Fokked Lightning. 



These present themselves under the form of a thin trail of white 

 light ; very defined ; sinuous in its course; able to divide into two, 

 and more rarely, into three branches ; directing themselves gener- 

 ally toward the earth, but frequently they dart from one group of 

 clouds to another. 



The clouds and the earth, or two oppositely electrified clouds, cor- 

 respond to the coatings of a leyden jar and the intervening air, the 

 glass of the jar ; the thunder storm is a charging and discharging 

 of a huge system of this kind. The zigzag and forked conditions 

 are undoubtedly due to the resistance which the discharges encounter 

 in the strata of air through which they pass. 



