2^24 
THE STATE OF THE SCIENCE OF ELECTRICITY. 
and that it is only prevented from doing so 
by the repulsive power of the electric fluid 
with which all bodies are charged or fllled in 
their natural state. 
Others, not content with this explanation, 
have recourse to another theory, proposed by 
Du Fay, which assumes that there are two 
electric fluids, one called the vitreous and the 
other the resinous. The explanation of this 
theory is a mere repetition of the flrst with a 
change of terms, vitreous being substituted 
for positive, and resinous for negative elec- 
tricity. However, as a clear comprehension 
of the known laws of electricity is essential 
to a right understanding of this theory of the 
solar system, we will state Du Fay’s theory 
of the two electricities : — ; 
1. If a cylinder of smoo'th glass is excited 
by friction, vitreous electricity is obtained. 
2. If a cylinder of sealing-wax is excited, 
resinous electricity is obtained. 
3. Two bodies charged with vitreous elec- 
tricity will repel each otner. 
4. Twm bodies charged with resinous elec- 
tricity will repel each other. 
5. Two bodies, the one charged with vi- 
treous and the other with resinous electri- 
city, will attract each other. 
The state of our knowledge in the science 
of electricity is not sufficiently advanced to 
enable scientific men to pronounce with cer- 
tainty which of these two theories is the true 
one, although Du Fay’s is generally consi- 
dered to be nearest the truth ; but Frank- 
lin’s is often preferred in treating on the 
subject, on account of its greater simplicity, 
and on that account we shall adopt Frank- 
lin’s terms of positive and negative in the 
present case, without offering any opinion 
as to the truth of either theory. We should 
prefer that of Du Fay, and are of opinion 
that it would square much better with our 
own than Franklin’s ; but minds unaccus- 
tomed to the science are apt to get confused 
amongst the various substances having 
greater affinities for the one or the other 
species of electricity. To the scientific read- 
er either theory is alike acceptable, as he can 
readily change the terms, and the application 
becomes nearly the same. 
Setting aside all theory for the present, 
we will proceed to examine such general 
facts relating to the science of electricity as 
have been developed and confirmed by the 
experiments of scientific men. These gene- 
ral facts are usually reduced to the six fol- 
lowing heads: — 1. Excitation; 2. Attrac- 
tion ; 3. Repulsion ; 4. Distribution ; 5. 
Transference ; 6. I nductioil. 
1. Excitation — “ If a piece of amber or 
sealing-wax or a smooth surface of glass, 
perfectly clean and dry, be briskly rubbed 
with a dry woollen cloth, and immediately 
after held over small light bodies, such as 
pieces of paper, thread, cork, straw, feathers, 
or fragments of gold leaf, strewed upon a 
table, these bodies will be seen to fly to- 
wards the surface that has been rubbed, and 
adhere to it for a certain time. The sur- 
faces which have acquired by friction this 
attractive power, are said to be excited^ and 
the substances, thus susceptible of excita- 
tion, are termed eZecfncs, in contra-distinction 
to such as are not excitable by a similar 
process, and which are therefore termed 
non-electrics.'^ In the tables of conducting 
and non-conducting bodies, gold is usually 
placed at the head of the list of non-electrics, 
and is considered the best known conductor 
of electricity ; at the head of the list of 
electrics is placed gum-lac, which is consi- 
dered the best insulating body or non-con- 
ductor. But in the electrical machines, a 
glass cylinder is commonly used as an electric, 
and a hollow brass cone, each end terminat- 
ing in a hemisphere, as a conductor. The 
glass cylinder is mounted on an axis and 
supported by two glass pillars, for the pur- 
pose of insulating it or cutting off the com- 
munication between the cylinder and the 
earth, as electricity will not pass through 
the glass pillars, that substance being a non- 
conductor. The handle by which the cylin- 
der is turned must also be of glass, otherwise 
the electricity will pass into the earth through 
the arm and body of the operator. These 
arrangements being made, if the handle be 
turned round briskly, and a piece of silk or 
woollen cloth be held against the cylinder 
with a pressure sufficient to cause a mode- 
rate degree of friction upon the surface of 
the glass, electricity will be accumulated in 
the cylinder. This is the process of excita- 
tion. We know nothing whatever of the 
nature of this process ; all that we know 
is, that with the same arrangements and 
means electricity is invariably accumulated 
in the glass cylinder, and that is sufficient 
for our present purpose. 
2 and 3. ATTRACTION AND REPULSION. 
— ^The glass cylinder being now charged with 
positive electricity, or filled with electric 
fluid, will attract the metallic conductor, which 
is in its natural state ; but if the conductor be 
negatively charged or emptied of the electric 
fluid, the attraction between the two bodies 
will be proportionately more powerful and 
intense ; if the negative conductor be now 
presented to the positive electric, a portion 
of the redundant fluid will be transferred to 
the conductor, and the two bodies being 
both positively electrified, will repel each 
other ; the same effect will be produced if 
the bodies are placed at a certain distance, 
and a metal ball suspended between by means 
of a silk thread, or any other insulating sub- 
stance, the ball will be attracted and repelled 
by each, alternately, until the electric fluid is 
reduced to an equilibrium in the two bodies, 
the ball extracting the fluid from the full 
body and carrying it to the empty one until 
this is accomplished. The manner in which 
this is effected must be particularly noted, as 
we shall have occasion to refer to it when we 
come to treat of comets. 
4. DISTRIBUTION. — It has been ascertain- 
ed by experiment, that in bodies charged 
with electricity, it is not distributed equally 
throughout the mass, the quantity a body is 
capable of receiving, depending more upon 
the extent of surface than the soild contents ; 
