234 ELEMENTARY LESSONS ON [CHAP. iv. 



original energy. The spark which passes in the 

 operation of dividing the charge is, indeed, evidence of 

 the loss of energy ; it is about half as powerful as the 

 spark would have been if the first jar had been simply 

 discharged, and it is just twice as powerful as the small 

 sparks yielded finally by the discharge of each jar after 

 the charge has been shared between them. 



The energy of a charge of the jar manifests itself, 

 as stated above, by the production of a spark at dis- 

 charge ; the sound, light, and heat produced being the 

 equivalent of the energy stored up. If discharge is 

 effected slowly through a long thin wire of high resistance 

 the air spark may be feeble, but the wire may be 

 perceptibly heated. A wet string being a feeble con- 

 ductor affords a slow and almost silent discharge ; here 

 probably the electrolytic conduction of the moisture is 

 accompanied by an action resembling that of secondary 

 batteries (Lesson XXXVIII.) tending to prolong the 

 duration of the discharge. 



279. Charge of Jars arranged in Cascade. 

 Franklin suggested that a series of jars might be 

 arranged, the outer coating of one being connected with 

 the inner one of the next, the outer coating of the last 

 being connected to earth. The object of this arrange- 

 ment was that the second jar might be charged with the 

 electricity repelled from the outer coating of the first, 

 the third from that of the second, and so on. This 

 " cascade " arrangement, however, is of no advantage, 

 the whole charge accumulated in the series being only 

 equal to that of one single jar. For if the inner coating 

 of the first jar be raised to V, that of the outer coating 

 of the last jar remaining at zero in contact with earth, 

 the difference of potential between the outer and inner 

 coating of any one jar will be only V, where n is 

 number of jars. And as the charge in each jar is equal 

 to its capacity C, multiplied by its potential, the charge 

 in each will only be -CV, and in the whole n jars the 



