002 
to pass through a hole in a plate of glass, one- 
twelfth 01 one-sixth ot an inch in diameter, 
t/y which means it will be more compact and 
powerful. By wetting the part round the 
note, the spark, by converting this into va- 
pour, may be conveyed to a greater dis- 
tance, with an increase ot rapidity, attended 
with a louder noise than common. Mr. 
Morgan, by attending to these and some 
other circumstances, has melted w ires, &c. 
15y the means of small bottles. 
If the charge ot a strong battery is passed 
through two or three inches of small wire, 
the latter will sometimes appear red-hot, first 
at the positive side ; and the redness will 
proceed towards the other end. 
It a battery is discharged through a small 
steel needle, it will, if the charge is strong, 
communicate magnetism to the needle. 
It the discharge of a battery passes through 
a small magnetic needle, it will destroy the 
polarity ot the needle, and sometimes invert 
the poles ; but it is otten necessary to repeat 
this several times. 
Dr. Priestley could melt nine inches of 
small iron wire at the distance of fifteen feet, 
but at the distance of twenty feet he could 
only make six inches of it red-hot, so that we ' 
may infer from this, that notwithstanding 
their conducting power, still metals resist in 
some degree the passage of the electric 
1 uid, and therefore in estimating the con- 
ducting powers ot different substances, their 
length must not be forgotten. 
It a slender wire is inclosed in a glass tube, 
and a battery discharged through this wire, 
it will be throwm into globules of different 
sizes, which may be collected from the inner 
surface of the tube ; they are often hollow, 
and little more than the scoria or dross of the 
metal. 
Dr. W atson and some other gentlemen 
made several curious experiments to ascer- 
tain the distance to which the electric shock 
might be conveyed, and the velocity of its 
motion, which may be briefly mentioned. 
In the first experiment, the shock was given, 
and spirits inflamed by the electric matter 
which had been conveyed through the river 
I hames. In another experiment, the elec- 
tric fluid was made to pass through a circuit 
of two miles, crossing the New River twice, 
going over several gravel-pits anti a large field, 
and afterwards conveyed through a circuit 
ot four miles. This motion was so instan- 
taneously performed by the electric fluid, 
that an observer, in the middle of a circuit 
oi two miles, felt himself shocked at the same 
instant that he saw the phial discharged. 
V. The instruments for ascertaining the 
presence and the quantity of electricity in 
different bodies, are various. The simplest 
of all is a pair ot little balls of cork, or rather 
ot the pith of the elder, which is still lighter, 
and suspended by silk threads. When 
broughtinto contact with an electrified body, 
the balls will immediately diverge, and ac- 
cording to the degree of divergence, a judg- 
ment is formed of the degree in which the 
body in question is electrified. A similar 
effect will be produced by a light and downy 
feather. J he pith-balls have received the 
name of Canton’s electrometer, from the 
ingenious electrician who first employed 
them for this purpose, and they are found 
useful in many experiments, 
for a more accurate admeasurement, that 
ELECTRICITY. 
is, f or ascertaining precisely the degree in 
which any body is electrified, an instrument 
somewhat less simple is required, and Hen- 
ley’s quadrant electrometer is in most gene- 
ral use. It consists (fig. 15.) of a perpendi- 
cular stem formed at top like a ball, and fur- 
nished at its lower end with a brass ferule 
and pin, by which it may be fixed in a 
hole made in the conductor, as at fig. 1. or 
at the top of a Leyden bottle. To the up- 
per part ot the stem, a graduated ivory 
semicircle is fixed, about the middle of which 
is a brass arm or cock, to support the axis of 
the index. r I he index Is a very slender 
stick, w’hich reaches from the centre of the 
graduated arch to the brass ferule ; and to 
its lower extremity is fastened a small pith- 
ball nicely turned in a lathe. When this 
electrometer is in a perpendicular position, 
and not electrified, the index hangs parallel 
to the pillar ; but when it is electrified, the 
index recedes more or less, according to the 
quantity of electricity. 
Lane’s discharging electrometer, as it is 
commonly called, is employed chiefly by 
the practitioners of medical electricity. 
It is represented by F D E, in fig. 16 , and 
is fixed to the wire that proceeds from the 
inside of the jar Z. The ball B touches the 
prime conductor A, which is supposed to 
stand before an electrical machine, fig. I. 
I he electrometer consists in a glass rod F D, 
furnished with brass caps F, D : from the lat- 
ter proceeds a strong brass wire, to which is 
attached an horizontal spring-socket: through 
this, the wire C E, having the ball C at one 
end, and the open ring E at the other, may 
be slided backwards and forwards, so as to 
place the ball C at any required distance 
from tlie ball B. Suppose the distance be- 
tween B and C to be -jjth of an inch or less, 
and that by means of a chain X, a communi- 
cation be formed from E to the outside coat- 
ing of the jar. When the jar is charged so 
high that the fluid can leap from B to C, the 
discharge will take place, and the r-troke pass 
through X from the inside to the outside of 
the jar. When the shocks are to be given 
through any part of the body, as the arm, 
then, instead of the chain ‘X, wires EL 
and I L are to be fastened, one to the ring 
E, and the other to a hook at I of the stand 
II I which communicates with the outside of 
the jar. The other extremities of the wire 
must be fastened to the directors K, L, 
which consist of brass wires and balls as L 
fastened into glass handles K, see also fig. 1 1 . 
The mode of operation is easily understood 
from a view of the figure (16), 'for when the 
chain X is away, the electric fluid must, in 
passing from the inside of the jars to the out- 
side, go through the w’ire E L ; the brass of 
the director ; the part of the arm between 
the balls of the directors ; and through the 
wire L I. By moving C nearer to, or farther 
from B, the strength of the shocks will be 
regulated to any degree. 
1 lie instrument represented in fig. 1 7, has 
been used successfully in the cure of the 
tooth-ache. A is a strong piece of box-wood 
in which the wires a b c and ef are fixed and 
then bent, the tooth and gum are placed be- 
tween c and/, and the circuit between the 
outside and inside of the jar is to be made 
by means of the chains g and h, which may 
be fastened in the same manner as the wires 
E L and I L in fig. 16 , aud by bringing C 
very near to B so as not absolutely to touch, 
the shocks which pass through the tooth and 
gum will be very slight. 
Several instruments have also been invent- 
ed for ascertaining the state of the atmo- 
sphere with respect to the quantity of elec- 
tricity it may contain, at any given time. 
The best of them are improvements upon 
Canton’s electrometer, which is made by in- 
closing the pith-balls, or rather two slips of 
gold leaf, in.a cylindrical glass vessel, to pre- 
vent their being affected by the wind. 
Bennet’s electrometer, fig. 18. is a very 
delicate instrument, and capable of distin- 
guishing small quantities of electricity. It 
consists of two slips of leaf gold A, suspended 
in a glass B. The foot C maybe of wood or 
-metal ; the cup D of metal. The cup is 
made Hat on the top, that plates, books > eva- 
porating water, or other things to be elec- 
trified, may be conveniently placed upon it. 
The cup is about an inch wider in diameter 
than the glass, and its rim about three quar- 
ters of an inch broad; which hangs parallel 
to the glass, to turn off the rain, and keep it 
sufficiently insulated. Within this is another 
circular rim, about half as broad as the other, 
which is lined with silk or velvet, and fits 
close upon the outside of the glass; thus the 
cap fits well, and may be easily taken off to 
repair any accident happening to the leaf 
gold. Within this rim is a tin tube, hanging 
from the centre of the cap, somewhat longer 
than the depth of the inner rim. In the 
tube a small peg is placed, and may be oc- 
casionally taken out. To the pt?g, which is 
made round at one end and fiat at the other, 
the slips of leaf gold are fastened with paste, 
gum-water, or varnish. These slips suspend- 
ed by the peg, and that in the tube fast to 
the centre of the cap, hang in the middle of 
the glass, about three inches long, and a 
quarter of an inch broad. On one side of 
the cap there is a small hole to place wires in. 
It is evident, that w ithout the glass, the leaf 
gold would be so agitated by the least mo- 
tion of the air, that it would be useless : and 
if the electricity should be communicated to 
the surface of the glass, it would interfere 
with the repulsion of the leaf gold ; there- 
fore two long pieces, H H, of tin-foil are 
fastened with varnish on opposite sides of the 
internal surface of the glass, where the leaf 
gold may be expected^to strike, and in con- 
nection with the foot. The upper end of 
the glass is covered and lined with sealing- 
wax as low as the outermost rim, to make its 
insulation more perfect. 
The sensibility of this instrument is so 
great as even fo astonish the most experi- 
enced electricians who have been witnesses 
of its effects. The brush of a feather, the 
throwing of chalk, hair-powder, or dust, 
against its cap, evince strong signs of elec- 
tricity. The electricity of vapour is ele- 
gantly shewn by pouring a tea-spoonful of 
water on an ignited coal placed in a metallic 
cup upon the cap of this electrometer ; and 
a very great and pleasing variety of other 
experiments may be made with this excellent 
instrument. 
“ In performing several atmospherico-elec- 
trical experiments about the year 1776, I 
found,” says Mr. Cavallo, “ that the use of 
Canton’s cork-ball electrometer w T as much 
obstructed by the wind, in consequence of 
which I attempted to inclose it in a bottle. 
