THUNDER AM) THE LIGHTNING-ROD 17:i 



which, wlu'ii mixed, remain inert, but, separated 

 from each other, manifest their wonderful proper- 

 and their violent tendency to recombination. 

 Rubbing is one way of effecting the separation of the 

 two electric principles, but it is far from being the 

 only one. Every radical change in the inmost na- 

 ture of a body also causes a manifestation of the two 

 electricities. So clouds, which are water changed 

 into vapor by the sun's heat, are often found to be 

 electrified. 



When two v differently electrified clouds come 

 near together, immediately their contrary electrici- 

 ties run toward each other to recombine, and with a 

 loud report there is a burst of flame that throws a 

 bright and sudden light. This light is lightning; 

 this burst of flame is a thunderbolt; the noise of the 

 explosion is thunder. Finally, the electric spark 

 can dart from a cloud electrified in one way to a spot 

 on the ground electrified in the other. 



" Generally you know a thunderbolt only by the 

 sudden illumination it produces and the crash of its 

 explosion. To see the thunderbolt itself you must 

 ovrrcome an unwarranted fear and look attentively 

 at the clouds, the center of the storm. From mo- 

 ment to moment you can see a dazzling streak of 

 light, simple or ramified, and of very irregular sin- 

 uous shape. A glowing furnace, metals at white 

 heat, have not its brilliancy; the sun alone furnishes 

 a comparison worthy the sovereign splendor of the 

 thunderbolt." 



'I saw tin thunderbolt," put in Jules, "when it 

 <tru<k the Jiir pi n ,. the day of the storm. For a 



