ELECTRICITY. 
and after a variety of trials and alterations 
the instrument was in the year 1777 brought 
to the state which is represented in fig. 19. 
The three parts of the ligure represent the 
instrument in its case, the same out of the 
case, and a section of its brass cap and neck. 
“ CDMN is an open glass vessel narrower 
at top than at bottom, and cemented into the 
wooden piece A B, by which part the instru- 
ment is held when it is to be presented to 
the atmosphere, or it may be rested upon a 
table for other experiments. This wooden 
piece also serves to screw the instrument 
into its wooden case O. The upper part of 
CDMN is tapering like the neck of a phial ; 
and a short glass tube is cemented into it, 
so as to project a little above and a little 
within tire neck of the former : then the up- 
per part of the instrument from C D to L, 
is covered with sealing-wax, by means of 
heat, which gives it the appearance of one 
contirmate body. The inner part G of the 
small glass tube is also covered with sealing- 
wax. Into this tube a brass wire is cement- 
ed, the lower part H of which is flattened, 
and is perforated with two holes ; the upper 
part L is formed into a screw, upon which 
the brass cap E F is screwed. The ollice 
of this cap is to defend the upper part of the 
instrument from the rain, lhe conical, or 
oval, or globular, corks P of this electrome- 
ter, are as small as can be made, and are 
suspended by exceedingly fine silver wires, 
the upper parts of which are formed in rings, 
which pass through the holes at II, and are 
thereby so loosely suspended, that they are 
caused to diverge when the brass cap E is 
exposed to a very slightly electrified atmo- 
sphere. I M and K N are two narrow slips 
of tin-foil stuck to the inside of the glass, and 
communicating with the wooden bottom 
A B ; they serve to carry off that electri- 
city, which, when the corks touch the glass, 
is communicated to it, and if accumulated 
would disturb the free motion of the corks.” 
VI. It is remarkable, that in certain cases 
bodies electrified will retain their electric 
power for almost any length of time, and on 
tiiis principle a very ingenious instrument 
has been constructed, called an electro- 
phorus. 
This simple species of electrical machine 
consists of two plates (fig. 20.) A and B, made 
of a circular form, from eight to eighteen 
inches in diameter, or upwards. The upper 
plate is generally made of brass ; but a tin 
plate, with a wire turned in upon its edge, 
will answer exceedingly well. At the centre 
of this plate there is a socket O, in which a 
glass handle I, nine or ten inches long, is 
fixed. A thin board, covered with tin-foil, 
and suspended by silken strings, will answer 
well, when the electrophorus is wanted of 
a large diameter. 
The under plate may be made of glass, 
sealing-wax, or the following composition, 
viz. four parts rosin, three parts pitch, three 
parts shell lac, two parts Venice turpentine, 
melted together over a gentle fire. It may 
be poured and spread upon a thin linen 
cloth, to about one-fourth of an inch thick. 
The linen doth must be stretched upon a 
hoop, and made as tight as possible. li the 
surface is a little rough, it will be no worse. 
The manner of using this machine is as 
follows : Rub the coated side of the under 
plate A with fine new flannel, or a hare’s or 
cat’s skin ; and when it is excited as much 
as possible, set it on a table, and place the 
upper plate upon it, and put your finger on 
the upper plate ; then remove your finger, 
and take hold of the top of the glass handle 
I, and apply it to the knob of a coated jar. 
Rep eat this operation for 30 or 40 times, 
and the jar will become charged. 
Cavallo mentions one of the above kind 
made by him, with which he charged a coat- 
ed phial several times, by once exciting, so 
strong as to pierce a hole through a card at 
every’ discharge. 
When a glass is covered with sealing-wax, 
after it is excited and laid with the waxed 
side dowmward, and the glass uppermost, 
then on making the usual experiment of put- 
ting the metal plate on it, and taking the 
spark, cVc. it will be attended with contrary- 
electricity to what it had before. 
To explain these phenomena it will be 
again necessary to recur to what lias been 
said concerning negative and positive elec- 
tricity ; it will be necessary also to recollect, 
that the negative electricity was originally 
termed the resinous, because it w r as first 
thought to be peculiar to those substances 
In the electrophorus, therefore, the lower 
part or resinous mass, being negatively elec- 
trified, the matter is taken from the metal 
plate, and this becoming also negatively 
electrified, the fluid is attracted from any 
body r which is presented to it. 
Electrical phenomena . — The various phe- 
nomena of electricity may, for the sake of 
perspicuity, be divided into four classes ; in 
the first of which may be included all those 
experiments which serve to illustrate the 
electrical attraction and repulsion ; in 
the second, those produced by the stream 
of electricity ; in the third class may be 
ranged all those phenomena which are ac 
companied with the luminous appearances 
and lastly, we may enumerate those more 
formidable effects arising from the concen 
trated electricity, in the experiments with 
the Leyden phial and the electrical battery. 
1. That light bodies are attracted and re 
pelled by the electrical influence, is evident 
from many common experiments, if a fea- 
ther of a" downy kind is affixed by linen 
threads to a small wire, and the wire is in 
serted into the prime conductor, upon turn 
ing the cylinder, the plumage will be found 
to expand every way, and the threads will 
also recede as far as possible from each 
other. If a finger approaches the feather, 
the plumage will bend towards it, and if the 
finger is moved, the feather will seem to 
follow it. If a spark is taken from the con- 
ductor, the plumage immediately collapses : 
and, if the cylinder is again excited, the 
threads will diverge, and the plumage ex- 
pand as before. 
There is another very entertaining expe- 
riment illustrative of the electric attraction. 
If a small plate of metal is suspended from 
the prime conductor, and another plate is 
placed at a small distance under it ; if then 
on the lower plate a piece of leaf gold is laid, 
when the cylinder is turned the gold will be 
lifted up, and expand itself with one corner 
opposite the upper and the other opposite 
the under plate. If the room is darkened, 
the leaf gold will appear to be supported by 
pillars of fire. 
003 
If instead of the leaf gold small figures of 
images (which may be easily made of thick 
paper or thin pasteboard, see tig. 21.) are 
placed on the under plate, after turning the 
cylinder the images will successively rise up 
hi an erect position, and will seem to dance 
between the two plates, sometimes leaping 
upon each other, and exhibiting themselves 
in a variety of entertaining positions, if the 
head of the image is held before the fire and 
dried, the image will ascend to the upper 
plate and remain there ; and if the experi- 
ment is reversed, and the feet of the image 
are dried, and the head a little moistened at 
the same time, the image will continue to 
stand immoveable on the lower plate, i he 
experiment will not succeed, if instead of 
metal, the images are placed upon glass, be- 
cause glass is an electric, and does not trans- 
mit the electrical matter, and consequently 
the images will not move backwards and for- 
wards ; but if the finger or any conducting 
body is held under the glass plate, they will 
then move as before. 
There 13 another very pretty experiment 
illustrative of the same principle, the appara- 
tus of which is to be found in the shops of 
most of the instrument-makers, and which 
lias been already described. It consists of 
three small bells, with clappers between 
them, (see fig. 8.) If the machine is turned 
the clappers fly from one bell to the other ^ 
and ring a kind of peal by the effect of elec- 
tricity. To explain this,' it is only necessary 
to notice that the two outer bells are sus- 
pended by metal chains, and the middle bell 
and clappers by silk, but from the middle 
bell a chain is suspended, which goes to the 
table. The fluid is then conveyed from the 
conductor down the chains to the two ex- 
terior bells, and the clappers which are light 
are attracted by them. The clappers then 
become charged and are repelled by the 
outer bells, but attracted by that in the 
middle, to which they give the electricity 
they had received, and it is conveyed to the 
earth by the chain which communicates with 
the table. Being thus disburdened, they 
are again attracted and strike the outer bells 
as before, and this is continued as long as 
the machine is in action. 
The electrical porcupine, as it has been 
called, is formed nearly in the shape of the 
animal, the name of which it bears. It is 
covered with ermine, or some other fur, in 
which are inserted some pieces of cotton 
pulled out to a considerable length, to re- 
semble the porcupine’s quills. On turning 
the machine the hairs of the fur or ermine 
diverge, and the pieces of cotton are dis- 
charged, and by a powerful conductor are 
driven to some feet distance. This effect, 
it is obvious, depends upon the principle 
which has been just explained, and is illus- 
trative of the electric repulsion. 
A very common mode of demonstrating 
the same’ effect, is to put a pointed W'ire into 
one of the holes of the conductor, and while 
the machine is in action, to hold a glass tum- 
bler over the point till its interior surface 
becomes charged. If then a few pith-balls 
are laid on the table, and covered with the 
tumbler, the balls will presently move about 
as if by magical power. See fig. 22. 
Electrified bodies in certain circumstances 
adhere so closely together, that the fact has 
given occasion to a new term in philosophy, 
4 G 2 
