ELE CTRI CiT Y. 
421 
8. If the eledtrophorus is not infulated, the cover, 
when put on, will give a {'park in the manner already men¬ 
tioned, and it will be fomewhat ftronger than when it. is 
infulated ; becaufe the fluid is allowed to efcape from the 
foie, and does not obftruct the entry into the cover. If 
we then, without removing the finger from the cover, 
touch the foie, nothing is felt ; but if we firft touch the 
foie, and, without removing the finger from it, touch the 
cover, we obtain a (hock. This is evident from the 
theory. By this feries of alternate touches, the period 
of the eledtrophorus is completed. The eledtrophorus 
is charged, or rendered neutral, by touching the plates 
when joined ; then, by touching both when leparated, 
the whole is reduced to the common (late. When fepa- 
rated, from being in the neutral (late, they have oppofite 
eledtricities, the foie (hewing that of the cake. When 
brought together, each in the common (late, they have 
oppofite eledtricities, the cover (hewing that of the cake. 
9. When, by long expofure to the air without its co¬ 
ver, the eledtrophorus has loft its virtue, it may be 
brought again into an adtive (late in a variety of ways. 
Its furface may be rendered negative by friction with dry 
cat or hare (kin, or warm flannel. It may be rendered 
negative by letting on it a jar charged negatively on the 
infide, and then touching the knob with any tiling com¬ 
municating with the ground. This is the molt expedi¬ 
tious method, and will give it a high degree of excita¬ 
tion, if the jar be of fize, and if the eledtrophorus be co¬ 
vered with a plate of tin-foil which comes into contadt 
all over its furface. This however requires the previous 
charging of the jar; therefore it will be as expeditious 
and effedtual to connedt this furface with the rubber of 
an eledtrical machine. 
The eledtrophorus has been compared to a charged 
plate of coated giafs. It is true that it may be brought 
into an external (fate which very much refembles, a 
charged pane ; namely, when the cover, in its natural 
(late, is let on the eledtrophorus in its natural (late ; and 
accordingly it gives a (hock, and the two exterior fur- 
faces become neutral ; but the internal conftitution, and 
the adting forces,.are totally and ejfcntially different. The 
two coatings of the pane would not, when feparated, ex¬ 
hibit the appearances of the eledtrophorus; nor, when 
touched in their disjoined (late, will they produce the 
fame effedts when joined. In the operation of coated 
giafs, the confhtnt or invariable part, the giafs is not hie 
agent, it is merely the occafion of the adtion, by allowing 
the accumulation. In the eledtrophorus, the electric, 
which is the conftant invaViable part, is the agent produc¬ 
ing the accumulation. The eledtrophorus is an original, 
and a very ingenious and curious, electrical machine. 
Nothing has fo much contributed to fpread fome general, 
though (light, acquaintance with the mechanical princi¬ 
ples of electricity. The numerous dabblers in natural 
knowledge had been diverted from fcientific purfuit by 
the variety of the lingular and amuling effedts of eledtri- 
city, and had really attained very little connedted know¬ 
ledge. The effedts of the eledtrophorus forced this 
knowledge upon them ; becaufe no life can be made of 
it without a pretty clear conception of the difpofition of 
the eledtricity, and the kind and intenfity of its adtion. 
It is therefore moft ungrateful in the experimenters who 
have attained better views, to attempt to rob Mr. Volta 
of the real merit of difeovery, by (hewing that its effedts 
are fimilar to thofe of Mr. Symmer’s dockings, or of 
Cigna’s plates, or of Franklin’s charged or diicharged 
giafs panes. And the attempt deftroys itfelf: for it 
lliews the ignorance or inattention of its author; for the 
fimilarity is not real, as cannot but appear clear to any 
perfon who will examine things minutely, and feientifi- 
cally. 
The eledtricians are no lefs obliged to Mr. Volta for 
another machine, or inftrument, from which the ftudy of 
nature’s operations has derived, or may derive, immenfe 
advantages. We mean' the condenser, or collector of 
Vol. VI. No. 361. 
ele/ilricity. This inftrument confifis of a fmooth metal 
plate, furnifhed with an infulating handle, and a femi- 
condudting, or imperfedtly infulating, plane. To ex¬ 
amine a weak eledtricity with this apparatus, as that of 
the air in calm and hot weather, which is not generally 
fenfible to an eledtrometer, the above-mentioned plate is 
to be placed upon the femi-condndting plane ; and a 
wire, or Come ether condudting fubitance, mult be con¬ 
nedted with the metal plate, and extended in the open 
air, fo as to abforb its electricity. The general effedit is 
to render fenfible an accumulation or deficiency of elec¬ 
tric fluid fo flight that it will not affect the moft delicate 
eledtrometer ; and it produces (at lead in the opinion of 
Mr. Volta) this eft'edt, by employing for the Cole, a body 
which is' an imperfedt conductor, fuch' as a plate of well 
dried, marble, or well dried, but not baked, wood ; or 
even a conducting body, covered with a piece of dry taf- 
fety or other filk. Mr. Volta, Cavalio, and others, who 
have written a great deal on the fubject, have attempted 
to (hew how thefe fubftances are preferable (and they 
certainly are preferable in a high degree) to more perfedt 
infulators; but, not having-taken pains to form pre- 
cife notions of the difpofition and adtion of the eledtric. 
fluid in the fituations afforded by the inftrument, their 
reafonings have, not been very clear. We think that an 
adequate conception of the effentials of an elcClrical con. 
denfator , may be acquired by means of the following con- 
fideratipns: 
Furnifh the cover of an eledtrophorus with a graduated 
eledtrometer, which indicates the proportional degrees of 
eleClricily ; eledtrify it pofitively to any degree, fuppo?e 
fix, while held in the hand, at fome diftance over a metal 
plate placed on a wine-glafs as an infulating (land, but 
communicating with the ground by a wire. Bring it 
gradually down toward the plate. Theory teaches, and 
we know it by experiment, that the eledtrometer will 
gradually fubfide, and perhaps will reach to 2 0 before 
the eledtricity is communicated in a fpark. Stop it be¬ 
fore this happens. In this (late the attraction of the plate 
produces a compenfation of four degrees of the mutual 
repullion of the parts of the cover, by conftipating the 
fluid on its under furface, and forming a deficient ftra- 
tum above. Now we can fuppofe that tIre efcape of the 
fluid from this body into the air begins as foon as elec¬ 
trified to the degree 6, and that it will fly to the plate 
with the degree 2, if brought nearer. If we can prevent 
thus communication to the plate, by interpofing an elec¬ 
tric, we may electrify the cover again, while fo near the 
metal plate, to the degree 6, before it will dream off into 
the air. If it be now removed from the plate, the fluid 
would raife the eledtrometer to xo, did it not immedi¬ 
ately dream off; and an eledtric excitement of any kind 
which could only raife this body to the degree 6 by its 
intenfity, will, by this apparatus, raife it to the degree 
10, if only copious enough in extent. If we do the fame 
thing when the wire is taken away which connedts the 
plate with the ground, we know that the fame diminu¬ 
tion of the eledtricity of the cover cannot be produced 
by bringing it down into the neighbourhood of the plate 
below. 
Here we fee the whole theory of Mr. Volta’s condenfer. 
He teems to have obi'eured his Conceptions of it by having 
his thoughts bent upon the eledtrophorus ; and is led 
into fruitlefs attempts to explain the advantages oi tire 
imperfedt condudtor above the perfedt infulator. But 
the apparatus is altogether different from an eledtro¬ 
phorus, and is more analogous in its operations to a 
coated plate not charged nor infulated on the oppofite 
fide ; and fuch a coated plate lying on a table is a com¬ 
plete condenfer, if the upper coating be of the fame fize 
with the plate of the condenfer. All the diredtions given 
by Mr. Volta for the preparation of the imperfedt con¬ 
dudtor fhew, that the e.tfedt produced is to make them as 
perfedt condudtors as .pofftble for any degree of eledtricity 
that exceeds a certain ,1mall intenfity, but fuch as (hall 
3 P not 
