456 



ELECTRICITY. 



~j. ! 



The electri- 

 city of the 

 outside 

 coating ne- 

 gative 

 when that 

 of the in- 

 ride ic po- 

 sitive, and 

 tin 



ntrfj*iv The mode of constructing batteries, and the precatt- 



Hfctnt-ity. t ; ons w |,ich are necessary in using them, will bo I'ully 



*"Y"" 11 ' detailed in the practical part of this article. It is enough 



to know, at present, that, by such combinations, clcc- 



tricity is capable of any degree of accumulation. 



SECT. VI. Phenomena of the Leyden Pliial. 



Is the preceding Section we have already had occa- 

 sion to mention the general construction and use of Un- 

 ion phial as a mean ot' accumulating tin- electric 

 fluid. It presents, however, many phenomena of a 

 very curious and instructive kind. 



It is obvious, that the external coating of die l.eydcn 

 phial has no communication whatever either with the 

 internal coating or with the conductor of the electri- 

 fying machine, and yet there is a manifest accumula- 

 tion of electricity on the outside of the glass, or in the 

 metallic coating which covers it It becomes, there- 

 fore, an interesting inquiry, to discover in what way 

 the electricity is communicated to the outside of the j-r. 

 whether the electricity is accumulated in the glass or in 

 the coating, what is the character of the internal and 

 external electricities, and in what manner they stand 

 related to each other. 



Dr Franklin, to whom we are indebted for almost 

 every' thing that has been done respecting the Leyden 

 phial, began his experiments by examining the inter- 

 nal and external electricities of the jar. Having sus- 

 pended a cork ball by n silken thread, he found that it 

 was attracted by the outside coating while it was re- 

 pelled by the inside coating, and that it was repelled 

 by the outside when it was attracted by the inside coat- 

 ing. Hence it followed, that the inside of the phial al- 

 ways possessed an opposite electricity to the outside, 

 the one being electrified positively when the other was 

 electrified negatively. This important conclusion v.-is 

 still better established, when Dr Franklin had observed 

 that he could charge a Leyden phial by holding it by 

 the brass knob, and presenting the external coating to 

 the prime conductor. When the phial was charged in 

 this way, the electricity of the external coating was po- 

 sitive, and that of the internal coating negative; and 

 when the phial was charged in the usual way by the 

 knobs, the internal coating was positive, and the exter- 

 nal one negative. 



When two phials were both charged through their 

 knobs, a cork ball, suspended between them by a silken 

 thread, was first attracted and then repelled by both 

 the knobs as they were positively electrified. When 

 Ixith the phials were charged through their outside coat- 

 ings, the ball was also repelled by them both ; but 

 when one of the phials was charged by its knob, and 

 the other by its outside coating, the suspended cork 

 ball played vigorously between them both, till the jars 

 were nearly discharged. Hence it follows, that the one 

 side of the phial possesses always the opposite elec- 

 tricity to the other, and that the two sides are simul- 

 taneously electrified, whether the electricity is drawn 

 from the prime conductor by the one side or the other. 



As glass is impenetrable to the electric fluid, it neces- 

 tlw negative sarily followed that the electricity was not communLca- 

 aitctriciry. ted from the one side of the glass to the other; and this 

 was easily ascertained by observing, that when the jar 

 was insulated it was not capable of being charged but 

 in a very trifling degree. Hence it followed, that the 

 electricity of the outside of the jar was supplied from 

 the earth by the conducting bodies which surrounded 

 it, and that whenever one side of an ck-ctric receives 



one kind of electricity, the opposite side i< simultane- 

 ously Mipplicd with the opjmsite electricity, cither from 

 the eurth or other conducting Ixxlics which are near it. 



The next object of Dr Franklin was, to .-i-ccrum it' 

 the |io-iti\c electricity of one side of the phial was 

 equal to the negative electricity of the other. For this 

 purpose he hung a small linen thread near the outside 

 dialing of a charged phial, and cwry time that he 

 presented his finger to the wire, the thread WHS attract- 

 ed by the coating, the electricity taken from the inside 

 by touching the wire being exactly cc|n.il to what was 

 drawn in on the outside by the thread. Professor Kich- 

 man obtained tile same re-ult by a very elegant expe- 

 riment. Having coated l>oth surfaces of a pane of 

 glass within two inches of its ed^e, he fixed linen 

 threads to the upper part of the coating on both sides. 

 When the plate was not charged, the linen threads 

 hung down in contact with. the coating; but when tin- 

 plate was placed in a vertical position and then char- 

 ged, the threads were re|H-lled from the coating, and 

 formed equal angles with it on both sides. When his 

 finger or any conductor was brought near one side, 

 the thread on the same side formed a less angle with 

 the coating, while the thread on the opposite side form- 

 ed an angle as much greater. Upon bringing hi.s finder 

 in contact with one of the sides, the corresponding 

 thread fell down upon the coating, while the opposite 

 thread formed twice the angle with the coating which 

 it had done before. The angle formed by the l\\ 

 threads with each other was therefore alwa\ s a constant 

 quantity. 



Dr Franklin at first imagined that the electricity accu- 

 mulated in the jar existed in tin in contact with 

 the glass, but he soon found upon farther examination, 

 that the electricity was contained in the ^la>s it-elf, 

 and that the sole use of the coating was, in the- act 

 of charging the jar, to conduct the electricity to all the 

 parts of the glass which was in. cont.-ict, and" in the act 

 of discharging it, to facilitate the communication be- 

 tween the two sides of the glass. In order to asi-ertain 

 these points, he charged a j.-ir, and placed it upon 

 or any insulating stand. He then took out the cork 

 and the wire, and ascertained that they did not contain 

 any electricity, by touching the outside coating with 

 one hand, and putting th<- finger of the other hand into 

 the mouth of the bottle, when he rcceixcd a shock as 

 powerful as if the wire and cor'; had been in their place. 

 Having put water into the phial, which being a con- 

 ductor, has nlways the same effect as a tinfoil coating, 

 he charged the jar, ami then pouring the water into an 

 insulated bottle, found that it also would not give the 

 shock. It then struck him, that the electricity must 

 either have gone off in the act of jxniring out the wa- 

 ter, or must still be resident in the buttle, lie there- 

 fore filled the phial with fresh water, and without 

 any new charge lie received the shock a^ before, which 

 completely proved that the electricity resided in the 

 glass. Dr Franklin made similar experiments with 

 coated panes of glass, and obtained the very same re- 

 sult, by changing the coating .-, he had changed the 

 water. The s;un<- truth may pcrhnps be more satisfac- 

 torily established by the following experiment. Fix. 

 the outside coating of an uncoutcd jar with a little 

 grease; and, instead of the inside coating, substitute a 

 <|iiantity of mercury, or of .small shot, or gold leaf, or 

 brass filings. As soon as it is charged, turn it upside 

 down, so as to allow the mercury or shot to fall out 

 along with tile wire and knob, and remove also the 

 outside coating. By this operation, the jar w ill not hav 



The pOMtivt 



thi- (>:, 



i -ji . .1 to the 



ny of 



the ot: 



II id mi an 't 

 experiment 

 in proof of 

 this. 



The tli-rlif: 



in die two 



op|Misite 

 Minorca at 



tilt ^lass, 

 a;u! not in 

 the couunji. 



