ELECTRICITY. 427 
greater or lefs quantity of the eleftric fluid, (the power of 
the machine being given,) proportional to the extent of 
flirfnce in the .conductor.—This refult appears by ob- 
ferving the difference in the magnitude and diftance of 
fparks- taken from a fmall conductor, and of thofe taken 
from a large one. There is a limit, however, beyond 
which this propofition vvilJ not hold true, but which, 
experiment has not yet fufficiently afcertained. For it is 
certain, that if the conductor be very long, it will dif- 
charge it'felf over the cylinder back to the rubber long 
before it is fully charged. The late Mr. G. C. Morgan 
affects, that by the mod powerful excitation of a cylinder 
fourteen inches in diameter, tire fpark afforded by_a con- 
-dufitor eight inches in diameter, and twelve feet long, 
did not equal half the length of that procured from the 
fame cylinder with a conductor of equal diameter, but 
fhortened to fix feet.- And he fuggefts that a conductor of 
half that length even, and about fixteen inches in diame¬ 
ter, would- have yielded a longer fpark than either of the 
preceding. See Morgan's Lett, on EleEl. vcd. i. p. 54, &c. 
IX; A body may be deprived of part of its natural por¬ 
tion of eledtric fluid ; that is, be negatively electrified.— 
If the rubber which communicates the fluid to the glafs 
cylinder, and from thence to the conductor, be infulated, 
becaufe by working the machine a quantity of its fluid 
is conveyed away, and it cannot receive a frefh fupply 
through its fupporter, it will be in an cxhavjfed or nega¬ 
tive ffate. If negative eleCtricity be required, then the 
chain which connects the rubber with furrounding ob¬ 
jects, and confequently with the earth, the great refer- 
voir of the eleCtric fluid, mu ft be removed from the in¬ 
fulated rubber, and hung to the prime conductor; for in 
this cafe the electricity of the conductor will be commu¬ 
nicated to the ground, and the rubber will appear ftrongly 
negative. Another conductor may be conneCted with the 
infulated rubber, and then as ftrong negative electricity 
may be obtained from this as pofitive can be in the cafe 
before-mentioned.—The patent machine of Mr. Nairne 
is admirably adapted for the purpofes both of pofitive and 
negative eleCtricity. 
X. When bodies are negatively electrified, they receive 
the eleCtric fluid from other bodies brought near them.— 
Let two infulated conductors, one of which is connected 
with the glafs cylinder, the other with the rubber, be 
■electrified ; whilft they are in this ftate let them be 
brought near each other; a fpark will pafs from that 
which (by Prop. VI.) is pofitively, to that which (by 
Prop. IX.) is negatively, electrified. — Let two per- 
fons (landing on g'laft feet be electrified, firft both pofi- 
lively, or both negatively, they will not, on contaCt, 
communicate the fluid to each other; but let them be 
eleCtrified, the one pofitively and the other negatively, 
by making a communication from one to the conductor, 
■and from the other to the rubber, on contaCt, the former 
will give, and the latter receive, a fpark. 
XI. From a pointed body pofitively eleCtrified, the fluid 
■will be feen to dream out, towards any eleCtrified body 
brought near it, in a conical pencil of rays ; whereas in 
palling from the uneleCtrified body to a pointed body ne¬ 
gatively eleCtrified, it will form a globular flame, or ftar, 
about its point.—This refult is made obvious by observ¬ 
ing, in a dark room, the different appearances of the elec¬ 
tric fluid at the extremity of a pointed wire, when the 
point is prefented to an infulated conductor pofitively, 
and when it is prefented to one negatively, eleCtrified; or 
•when fuch a wire is fixed upon a conductor pofitively or 
negatively eleCtrified. Within a luminous conductor elec¬ 
trified pofitively, (viewed in a dark room,) the eleCtric 
fluid will be feen paffing in the form of a pencil from one 
wire, and received in the form of a ftar upon the other; 
and the reverfe, if it be eleCtrified negatively. 
XII. If two bodies be electrified, both pofitively, or 
•both negatively, they repel each other; but if one be 
eleCtrified pofitively, and the other be negatively or not 
at all eleCtrified, they attract each other..—Thus, light 
feathers, or hair, connected with the conductor, appear 
repellent, but are attracted by bringing any nomelecbi- 
fied body near them. The hair of a per (on eleCtrified 
becomes repellent. In the graduated or Henley’s elec¬ 
trometer, the ball is repelled according to the degree in 
which the conductor is eleCtrified. Downy feathers, pa¬ 
per figures, threads of flax, thiftle down, gold leaf, brafs 
duft, or 01 her light bodies, brought near to the conductor, 
are alternately attracted and repelled. But this will not 
take place if the bodies be laid on a plate of glafs. 
Two bells being fufpended by wires from a brafs rod 
connected with the conductor, and a third by a filk cord, 
and two fmall balls of brafs fufpended by a filken thread 
between the bells, the eleCtric fluid will be communi¬ 
cated from the conductor to the outer bells, and by the 
balls to the middle bell, and from thence Conveyed by 
a chain to the earth : the balls in receiving and commu¬ 
nicating the fluid are attracted and repelled fucceffively, 
and produce tinging': exaCtly on the fame principle as 
the experiment made with the Leyden phial and fix bells, 
as (hewn in the EleCtricity Plate I. fig. 9. 
Let water flow from a capillary tube, from which, be¬ 
fore it is electrified, it pafi’es in drops; upon being elec¬ 
trified, the particles of fluid will be feparated, and their 
motion accelerated. Thefe appearances will be prefent¬ 
ed, whether the conductor be pofitively or negatively 
eleCtrified. 
Mr. Syrmner’s eleCtricity of filk ftockings illuftratcs 
this propofition. He had been accuftomed to wear two 
pair of filk ftockings, a white pair under black ones. 
When thefe were pulled off together, no (igns of eleCtri¬ 
city appeared, but on pulling off the black ones from the 
white, he heard a fnapping noife, and in the dark per¬ 
ceived luminous fparks. On this fubjeCt he has related 
a number of very curious experiments on the attraction 
and repulfion of the ftockings, and upon their different 
ftates of eleCtricity. 
Since it is found that rubbed glafs electrifies any infu¬ 
lated conductor pofitively, it may he determined whether 
any body is eleCtrified pofitively or negatively, by bring¬ 
ing it near to a pith-ball, or down-feather, pofitively 
eleCtrified, and observing whether the ball or feather be 
attratted, or repelled, by the body. Bring a pith-ball or 
down-feather, fufpended by a filken thread and pofitively 
eleCtrified by any rubbed glafs fur face, near to another 
pith-ball or feather fufpended by a flaxen thread from a 
conductor connected with the cylinder; then bring the 
lame near to a conductor connected with the rubber, and 
the kind or meafure of the eleCtricity will be feen. Thus 
was the invention.and utility of the clettrometer fuggefted. 
XIII. From the fliarp points of eleCtrified bodies there 
proceeds a current of air.-—A wire, with fliarp points 
bent in oppofite directions, and fufpended on the point 
of a perpendicular wire inferted in the conductor, will be 
carried round by the current of air proceeding from the 
points. Let feveral pieces of imbofied or gilt paper be 
(tuck like vanes into the fide of a cork, through the cen¬ 
ter of which a needle paffes; fufpend the whole by a 
magnet, and prefent one of the vanes to the point of a 
wire inferted in the conductor; they will be put into 
motion. 
The rapid diflipation of the eleCtric fluid by fliarp points, 
and the impoflibility of making any confiderable accumu¬ 
lation in a body which has,any fuch points projecting 
beyond other parts of its furfa.ee, is one of the mod ab- 
ftrufe phenomena in eleCtricity. The diflipation is at¬ 
tended with many remarkable circumftances, which have 
greatly the appearance of the aCtual efcape of fome ma¬ 
terial fubftance. A ftream of wind blows from fuch 
a point, and quickly electrifies the air of a room to fuch 
a degree, that an electrometer in the fartheft corner of 
the room is affeCted by it. This diflipation in a dark 
place is, in many inftances, accompanied by a bright train 
of light diverging from the point like a firework. Dr. 
Franklin is therefore very anxious to reconcile this ap¬ 
pearance 
