410 
ELECTRICITY. 
Of the ELECTRICAL APPARATUS. 
The electrical machine is the primum mobile of the elec¬ 
trical apparatus. It confifis of the electric or barrel, the 
moving engine or wheel, the rubber, and the prime con¬ 
ductor. I'n the early date of the fcience, for the elec¬ 
tric, was tiled fealing-vvax, firlplmr, or.rough glafs ; but, 
lince the method of initiating the rubber, and fo pro¬ 
ducing negative electricity, was introduced, fmooth glafs 
lias been it fed. The form is commonly either that of a 
globe, or of a cylinder. Each figure has its advantages, 
and its inconveniences. Dr. van Marttm, a late German 
writer, has conflnided a machine, in which gum-lac, in 
the form of a difc, is ufed as an electric inftead of glafs ; 
which has the effed of depending very little on the tem¬ 
perature of the air; defcribed in his Treatife concerning 
the method of electrifying. Groningen, 1776. But he 
lias fince procured others to be made by Mr. Cuthbert- 
J’on of London, conftru6ted of large difcs, or round plates 
of glafs : one of thefe is now placed in Teyler’s mufeum 
at Harlem, having two of thefe glafs plates, of (ixty-five 
inches diameter, excited, on both fides of them, by rub¬ 
bers of waxed taffaty ; with which effects are produced 
that are truly aftonilhing and tremendous. 
There have been various contrivances for giving motion 
to the electric of a machine. The common method is by 
a wheel turned by a winch or handle ; a cord going round 
a groove in the periphery of the wheel, and over a pul¬ 
ley in the neck of the globe or cylinder. Others have 
ufed multiplying wheels, which are eafily turned by a 
winch ; and others again make life of a wheel and pinion, 
or a wheel and endlefs fcrew. But Van Marum’s ma¬ 
chine is faid to have the completed movement, its ope¬ 
ration being very uniform, and eafily worked ; it is kept 
in motion by a weight, which, after being wound up to 
the height of twelve feet, continues the motion uniformly 
for fix hours ; yielding alfo a negative power, as well as 
the politive ; and the condudors annexed to it fet ving 
eafily to convey the eledrical fluid wherever it is requir¬ 
ed, without the addition of any chain, or wires, &c. 
The rubber is the next material part of a machine. 
Thefe were formerly made of'red bafil fkins, duffed with 
hair, wool, flax, or bran : Dr. Nooth introduced filk 
cufhions duffed with hair, over which is laid a piece of 
feather, rubbed with amalgam, which arc better than the 
others. The rubber may be infulated in any way that 
bed fuits the confirudion of the machine : and a chain 
or wire may eafily be fufpended from it, to communicate 
with the floor, whenever the infulation is not neced’ary; 
and thus politive and negative electricity may be pro¬ 
duced at pleafure. 
The prime conduElor is another neceffary appendage to 
the electrical machine : it is infulated, and fo connected 
with the eleclrical machine, as to receive the eledric 
fluid immediately from the excited eledric. In the pre- 
fent advanced date of the fcience, this part of the elec¬ 
trical apparatus has been confiderably improved. The 
prime condudor is commonly made of hollow brafs, of a 
cylindrical form, perfectly fmooth and round, without 
points or fliarp edges. The ends of the cqndudor are 
spherical; and it is neceffary, that the part mod remote 
from the eledric fliould be made round and much larger 
than the red, the better to prevent the eledric fluid from 
efcaping, which it always endeavours mod to do at the 
greate.lt didance .from the eledric or barrel : and the 
other end fhould be furniflied with feveral pointed wires 
or needles, either fufpended from, or fixed to, an open 
metallic ring, and pointing to the globe or cylinder, or 
plate, to colled: the eledric fluid. It is bed fupported 
by pillars of lblid glafs, covered with fealing-wax or 
.good varnifh. Prime condudors of a large fize are ufu- 
dly made of padeboard, covered with tin-foil or imbof- 
fed paper; thefe being ufeful for throwing off a longer 
and delifer fpark than thofe of a fmaller fize : they fliould 
terminate in a fmaller knob or obtufe edge, at which the 
fparks fhould be folicited. Mr. Nairne prepared a con- 
dudor fix feet in length, and one foot in diameter, from 
which he drew eledrical fparks at the didance of fix teen, 
feventeen, or eighteen, inches; and Dr. Van Marutn dill 
far exceeded this, with a condudor of eight inches dia¬ 
meter, and upwards of twenty feet long, formed of dif-, 
ferent pieces, and applied to the large eledrical machine 
in Teyler’s mufeum at Harlem, the mod powerful ma¬ 
chine of the kind yet condruded. But the fize of the 
condudor mud always be limited by that of the elcdric 
or barrel, there being a maximum which the fize of the 
former drould not exceed ; for it may be fo large, that 
the didipation of the eledric fluid from its furface may 
be greater than that which the eledric is capable of Rip- 
plying. 
Dr. Priefiley recommends a prime condudor of polifli- 
ed copper, in the form of a pear, fupported by a pillar 
and a firm bafis of baked wood : this receives the elec¬ 
tric fluid by a long arched wire of foft brafs, which may 
be eafily bent, and raifed or lowered to the globe or cy¬ 
linder ; it is terminated by an open ring, in which fome 
Iharp-pointed wires are hung. I11 the body of this con¬ 
dudor are holes for the infertion of metalline rods. This, 
he fays, colleds the eledric fluid perfedly well, and re¬ 
tains it equally every where. Hijl. ElcEl. vol. ii. fed. 2. 
Mr. Henley (Philof. Tranf. vol. lxiv. p. 403.) con¬ 
trived a new kind of prime condudor, which, from its 
life, is called the luminous condudor. It confids of a 
glafs tube eighteen inches long, and two inches diame¬ 
ter. The tube is furniflied at both ends with brafs caps 
and ferules about two inches long, cemented and made 
air-tight, and terminated by brafs balls. In one of thefe 
caps is drilled a fmall hole, which is covered by a flrong 
valve, and ferves for exhaufling the tube of its air. 
Within the tube at each end there is a knobbed wire, 
projeding to the didance of two inches and a half from 
the brafs caps. To one of the" balls is annexed a fine- 
pointed wire for receiving and collecting the eledriG 
fluid, and to the other a wire with a knob or ball for dif- 
chargi'ng it. The condudor, thus prepared, is fupported 
on pillars of fealing-wax or glafs. Betide the common 
purpofe.s of a prime condudor to an eledrical machine, 
this apparatus ferves to exhibit and afeertain the direc¬ 
tion of the eledric fluid in its palfage through it. 
The mod approved-eledrical machines are exhibited in 
the Eledricity Plate I. Fig. 1, reprefents the very ingenious 
eledrical machine invented by Mr. Read, and improved 
by Mr. Lane. The glafs cylinder A, is moved vertically 
by means of the pulley at the lower end of the axis, the 
pulley being turned by the large wheel B, parallel to the 
table : there are feveral pulleys, of different fizes, either 
of which may be ufed, according as the motion is required 
to be quicker or flower. The prime condudor C is fur¬ 
niflied with points to colled the eledric fluid, and is 
icrewed to the wire of a coated jar D. The figure fliews 
alfo the manner of applying Mr. Lane’s eledrometer, 
which is ferewed on to the prime condudor at K, as will 
be hereafter explained. 
Fig. 2, reprefents Dr. Priedley’s machine, defcribed in 
his Hidory of Eledricity ; in which g is the globe, or 
eledric ; f the rubber ; in the two pillars d, d> of baked 
wood, are feveral boles to receive the fpindles of dif¬ 
ferent globes or cylinders, feveral of which may be put 
on together, to increafe the eledricity : him is the prime 
condudor, being a copper tube, fupported on a fland of 
glafs or baked wood. 
Fig- 3) ' s a portable eledrical machine for common 
ufes. C reprefents the. eledric, or glafs cylinder, about 
one foot in diameter, and twenty inches long, which is 
turned by means of a wheel; the rubber or cufliion is 
fupported behind the cylinder by two upright fprings 
that appear beneath, and are fadened to two crols bars 
of glals. B, is a metallic prime condudor, fupported 
on two pillars of glafs : from the end neared to the cy¬ 
linder ifiue feveral points, and at the other end the ball E 
a projeds 
