470 



Mr. Warreyi Be La Rue 



[Jan. 21, 



On the supposition that a cloud would act very much as a mere 

 point at the great distance at which a lightning discharge occurs 

 between clouds or a cloud and the earth, we may from these data 



Fig. 7. 



calculate the potential necessary to produce a lightning flash a mile, 

 or 63,360 inches, long. It would require nearly 243 units of 14,400 

 cells united in series,"'or say 3,500,000 cells about. 



The striking distance may be increased by an arrangement of 

 condensers to form what is called a cascade,* and in this way I shall 

 be able to produce a spark an inch long with only 1200 cells. Such a 

 battery I now use to charge twenty-five plates of a small condenser, and 

 by means of a rotating commutator, connect, so to speak, the outside 

 of one plate to the inside of the next, and thus multiply the potential 



* The battery itself is a cascade. 



