MACHINE, ELECTRIC. 
w ire terminating with a knob, considera1)ly 
above the mouth of the jar, fig. 4. 4^ hen 
it is required to be charged, it may be held 
in the hand, or placed on an uninsulated 
table, and the knob of the w ire applied to 
the conductor ; the inside coated siuface 
becomes possessed of the electricity of the 
conductor, and the external surface ac- 
quires the contrary electricity, by means of 
its uninsulated coating. When a jar ot this 
kind is highly charged, it will discharge 
spontaneously pver the uncoated surface, 
and seldom through the glass, whereas, when 
the uncoated surface is targe, it is more apt 
to break by that means, and become useless. 
Yet, there is no certainty that a jar, which 
has discharged 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 tlie 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 sustain 
a very high charge, and produce much 
greater effects than one of the last descrip- 
tion. The charging wire being inserted 
loosely into the tube, wilt fall out on invert- 
ing the jar, and tire charge will remain for 
several weeks without much loss. A jar 
thus charged, may be put into the pocket, 
and applied to many purposes that the com- 
mon 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 chaj-ge 
pearly one-third greater than in the ordi- 
nary state. 
When a greater degree of electric force is 
required, lar ger jars must be used, in which 
the form is of no consequence, except as far 
as relates to converrience. But it is less 
expensive, and nearly as effectual, to use a 
number of smaller jars, having the same 
quantity of coated surface as the large jars. 
In this case, a communication must be 
formed between all the orrtside coatings, 
which may be done by placing them on a 
stand of metal ; and also between all the 
inner coatings, which is best done by means 
of wires. Such a collection is called a bat- 
tery, aitd may be charged and discharged 
like a siirgle jar, fig. 5. 
In dischaiging electrical jars, the elec- 
tricity goes in the greatest quantity through 
the best conductors, and' by the shortest 
course. Tims, if a chain and a wire, com- 
municating with the outer coating, be pre- 
sented 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 con- 
ductor, 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 considerable 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 
tlie force of the electric shock is weakened, 
that is, its effects are dimininished, by using 
a conductor of great length in making the 
discharge. Ur. Watson, and other gentle- 
men 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 
transmitted instantaneously through the 
length of 12,276 feet. 
When any animal or substance is to be 
subjected to the shock, it is done by means 
of two chains, one of which connects one 
extremity of the animal oi' substance with 
the outer coating, and the other being made 
to toucli the othei\ extremity, is applied to 
the knob of the inner coating to make tlie 
discharge. The animal or substance thus 
forming a part of the circuit, receives the 
whole shock. The strong shock of a bat- 
tery will melt wire of tlie seventieth of an 
inch in diameter, and wkes ofless diameters 
are frequently blown away and dispersed ; 
and the effect is the same witli equal quan- 
tities of electricity, whether the intensity be 
greater or less, within certain extended li- 
mits. Gunpowder may be fired by a charge 
of tliree square feet : the metliod is, to put 
it into a quill, and thrust a wire into each 
end, so as not to meet, and tlicri tnake these 
wires a part of the circuit. A less charge 
will serve if iron filings be mixed with the 
gunpowder. Alcohol, ether, or a mixture 
of common air and hydrogen may also be 
fired by the same means, or even by the 
spark from the conductor. 
If the ball of a thermometer be placed in 
q strong current of electricity, the mercury 
or spirit will rise many degrees. 
If a thill bottle be exhausted of air by 
means of the air-pump, it will receive a con- 
siderable charge by applying its bottom to 
