MACHINE, ELECTRIC. 



square feet of glass will deprive a man of 

 sensation for a time, if the head be made 

 a part of the circuit through which the 

 electricity moves. No inconvenience has 

 been found from the electric shock by 

 men of strong 1 habits ; but women of de- 

 licate constitutions have had convulsions 

 from a violent shock. It may be observed, 

 that the electric shock is a proof that the 

 electric matter can pass through the sub- 

 stance of non-electrics, and is not uni- 

 versally conducted along the surfaces 

 alone, as some have supposed. 



The object of the philosopher being, 

 in general, to collect a large quantity of 

 electricity, by means of the surfaces of 

 electrics, it is more usual to employ jars, 

 and not plates. These are made of va- 

 rious shapes and magnitudes ; but the 

 most useful are thin cylindrical glass ves- 

 sels, about four inches in diameter, and 

 fourteen in height, coated within and 

 without with tin-foil, which is stuck on 

 with gum-water, paste, or wax, excepting 

 two inches of the i-im or edge, which is* 

 left bare, to prevent the communication 

 between the coatings. About four inches 

 from the bottom, within, is a large cork, 

 that receives a thick wire, ending in seve- 

 ral ramifications, which touch the inside 

 coating ; the upper end of the wire ter- 

 minating with a knob, considerably above 

 the mouth of the jar, fig. 4. When it is 

 required to be charged, it may be held in 

 the hand, or placed on an uninsulated ta- 

 ble, and the knob of the wire applied to 

 the conductor ; the inside coated surface 

 becomes possessed of the electricity of 

 the conductor, and the external surface 

 acquires the contrary electricity, by 

 means of its uninsulated coating. When 

 a jar of this kind is highly charged, it will 

 discharge spontaneously over the uncoat- 

 ed surface, and seldom through the glass; 

 whereas, when the uncoated surface is 

 krge, it is more apt to break by that 

 means, and become useless. Yet there 

 is no certainty that a jar, which has dis- 

 charged itself over its surface, will not at 

 another time break by a discharge through 

 the glass, as the contrary often happens. 

 If paper covered with tin-foil be used for 

 the coating, with the paper next the 

 glass, the jar will be less liable to break. 



A jar of considerable thickness, with a 

 neck like a bottle, in which is cemented 

 a thick tube to receive the wire, will sus- 

 tain a very high charge, and produce 

 much greater effects than one of the last 

 description. The charging wire being 

 inserted loosely into the tube, will fall out 

 on inverting the jar, and the charge will 

 remain for several weeks without much 



VOL. iv. 



loss. A jar thus charged, may be put in- 

 to the pocket, and applied to many pur- 

 poses that the common jar cannot be used 

 for. 



If the inside of the jar be considerably 

 damped, by blowing into it, through a 

 tube reaching to the bottom, it will take 

 a charge nearly one-third greater than in 

 the ordinary state. 



When a greater degree of electric force 

 is required, larger jars must be used, in 

 which the form is of no consequence, ex- 

 cept as far as relates to convenience. But 

 it is less expensive, and nearby as effec- 

 tual, to use a number of smaller jars, hav- 

 ing; the same quantity of coated surface 

 as the large jars. In this case, a commu- 

 nication must be formed between all the 

 outside coaurjg-s, which may be done by 

 placing them on a stand of metal ; and 

 also between all the inner coalings, wliicti 

 is best done by means of wires. Such a 

 collection is called a battery, and may be 

 charged and discharged like a single jar, 

 fig- 5. 



In discharging electrical jars, the elec- 

 tricity goes in the greatest quantity 

 through the best conductors, and by the 

 shortest course. Thus, if a chain and a 

 wire, communicating with the outer coat- 

 ing, be presented to the knob of a jar, 

 the greater part of the charge will pass 

 by the wire, and very little by the chain, 

 which is a worse conductor, by reason of 

 its discontinuation at every link. When 

 the discharge is made by the chain only, 

 sparks are seen at every link, which is a 

 proof that they are not in contact ; and 

 as the chain must be stretched by a con- 

 siderable force before the sparks cease to 

 appear on the discharge, it follows, that 

 there is a repulsive power in bodies, by 

 which they are prevented from coming- 

 into contact, unless by means of a certain 

 force. 



By accurate experiments, it appears, 

 that the force of the electric shock is 

 weakened, that is, its effects are diminish- 

 ed, by using a conductor of great length 

 in making the discharge. Dr. Watson, 

 and other gentlemen of eminence in the 

 philosophical world, were at the pains of 

 making experiments of the same kind, 

 but much more accurate. They found, 

 by means of wire insulated on baked 

 wood, that the electric shock was trans- 

 mitted instantaneously through the length 

 of 12,276 feet. 



When any animator substance is to be 

 subjected to the shock, it is done by 

 means of two chains, one of which con- 

 nects one extremity of the animal or sub- 

 stance with the outer coating, and the 

 A a 



