ELECTRICITY. 



117 



is drawn out of the tail of the first serving to charge (the inside of) the second ; 

 what is driven out of the second charging the third, and so on."* 



In this way he constructed an electrical battery. After charging a series 

 of jars he separated them, putting the insides in metallic communication with 

 each other, and the outsides, in like manner, in metallic communication. By 

 si;ch means he obtained discharges sufficiently powerful to kill the smaller 

 animals. 



But the experiment which appeared to be most conclusive in the support 

 it gave to his hypothesis of the transfer of the electricity from the exterior to 

 the interior of the jar in the process of charging it, was the following : A jar 

 was suspended by its hook on the prime conductor of the machine, so that a 

 metallic communication was maintained between the conductor and the inside 

 of the jar. Meanwhile, the rubber was insulated. On working the machine, 

 the jar was found to receive no charge. A metallic wire was now rolled round 

 the outer coating of the jar, and carried thence to the rubber, so as to make a 

 communication between them, both being still, in other respects, insulated. 

 The jar was now charged with ease, which was explained by the supposition 

 that the electric fluid passed from the outside coating by the wire to the rubber, 

 and thence by the glass globe and prime conductor to the inside of the jar.f 



According to the hypothesis above stated, there is no essential distinction, 

 so far as relates to the charge, between the external coating and the internal 

 contents of the jar ; the one ought to be as easily charged as the other. This 

 was accordingly found to be the case. A jar was placed on an insulating sup- 

 port, and while the external coating was put in communication with the prime 

 conductor of the machine, the wire extending from the interior was put in com- 

 munication with the rubber. The electricity of the outer coating was now 

 positive, and that of the inside negative ; and the jar was discharged, and pro- 

 duced the same effects as before. 



The next important investigation was as to the place in which the electricity 

 of the jar was contained. To determine this, Franklin charged a jar, and in- 

 sulated it. He then removed the cork, and the wire by which the electricity 

 was conveyed from the machine to the inside of the jar. On examining these, 

 he found them free from electricity. He next carefully decanted the water 

 from the charged jar into another insulated vessel. On examining this it was 

 found to be free from electricity. Other water in its natural state was now 

 introduced into the charged jar to replace that which had been decanted ; and 

 on placing one hand on the outside coating, and the other in the water, he re- 

 ceived the shock as forcibly as if no change had been made in the jar since it 

 was first charged.^ 



A piece of glass was then placed between two plates of lead extending nearly 

 to its edge on every side. One of these plates of lead being touched by the 

 hand, the other was charged with electricity as usual. The plates were then 

 removed from the glass, and, being examined, were found to be in their natural 

 state. On presenting the finger to the glass where the lead had covered it, 

 little sparks were received ; and on displacing the lead and touching it at both 

 surfaces, a violent shock was received. 



From this he inferred that the glass was the substance in which the electri- 

 city was deposited ; and the metallic coating, or the water, or other conductor, 

 applied to it, " served only, like the armature of the loadstone, to unite the 

 forces of the several parts, and bring them at once to any point desired ; it be 

 ing the property of a non-electric [conductor], that the whole body instantly re 

 ceivesj or gives, what electrical fire is given to, or taken from any one of its parts. "|| 



From a very early period of the progress of electrical observations, the anal 



* Letters, p. 199. t Letters, p. 253. J Letters, p. 201. || Letters, p. 202. 



