LESSONS IN ELECTRICITY. 



FIG. 38. 



"with which you arc now so familiar will 

 enable you to thoroughly analyze and 

 understand the action of the Leydcn jar. 

 In charging- the jar the outer coating is 

 connected with the earth, and the inner 

 coating with the electrical machine. Let 

 the machine, as usual, be of glass yield- 

 ing positive electricity. When it is 

 worked the electricity poured into the jar 

 acts inductively across the glass upon the 

 outer coating, attracting its negative and 

 repelling its positive to the earth. Two 

 mutually attractive electric layers are thus 

 in presence of each other, being separa- 

 ted merely by the glass. When the ma- 

 chine is in good order and the glass of 

 the jar is thin, the attraction may be ren- 

 dered strong enough to perforate the jar. 

 By means of the discharger the opposite 

 electricities are enabled to unite in the 

 form of a F par If. 



Franklin saw and announced with clear- 

 ness the escape of the electricity from 

 the outer coating of the jar. His state- 

 ment is that whatever be the quantity of 

 the " electric fire" thrown into the jar, 

 an equal quantity was dislodged from the 

 outside. We have now to prove by ac- 

 tual experiment that this explanation is 

 correct. 



Place your Leydcn jar upon a, table, 

 and connect the outer coating with your 

 electroscope. There is no divergence of 

 the leaves when electricity is poured into 

 the jar. 



But here the outer coating is connect- 



ed through the table with the earth. Let 

 us cut off this communication by an in- 

 sulator. Place the jar upon a board up- 

 portcd by warm tumblers, or upon a 

 piece of vulcanized india-rubber cloth, 

 and again connect the outer coating with 

 the electroscope. The moment electric- 

 ity is communicated to the knob of the 

 jar the leaves of Dutch metal diverge. 

 Detach the wire by your discharger and 

 test the quality of the electricity it is 

 positive, as theory declares it must be. 



Consider now the experiment of Klcist 

 and Cumcus (fig. 04). You will, I doubt 

 not, penetrate its meaning. You will see 

 that in their case the liand formed the 

 outer coating of the jar. When elec- 

 tricity was communicated through the 

 nail to the water within, that electricity 

 acted across the glass inductively upon 

 the hand, attracting the ono fluid and 

 repelling the other to the earth. 



Again, I say, prove all things ; and 

 what is here affirmed may be proved by 

 the following beautiful and conclusive ex- 

 periment : Stand on your board, i i' fig. 

 39, insulated by its four tumblers ; or 

 upon a sheet of gutta-percha, or vulcan- 

 ized india-rubber. Seize the old Leyden 

 phial, j, with your left hand, and pre- 

 sent the knuckle of your right hand to 

 your balanced lath, L' L. When electric- 

 ity is communicated to the nail, the lath 

 i* immediately attracted by the knuckle. 

 Or touch your electroscope with your 

 right hand ; when the phial is charged 



