Cuap. VIL, § 5.] 
poles of the battery and became enfeebled with dis- 
tance from them, they used a language not quite 
rigorous indeed, yet expressing the actual pheno- 
mena with that general accuracy which we can alone 
expect in the first stages of so new and difficult an 
inquiry. “The sum of chemical decomposition is 
constant for any section of a decomposing conductor” 
is Dr Faraday’s expression. Sois the sum of illumi- 
nations arising from light radiating from a point, 
when taken across any section of its path, yet the 
influence is said to vary inversely as the square of 
its distance from the origin. The part of Dr Fara- 
day’s conclusions, however, most open to excep- 
tion, is what refers to electric action at a distance, 
which he conceives to depend solely upon induction 
acting on intervening particles, which induction may 
take place along curved lines, It is indeed true that 
he has shown, by a beautiful experiment, that the in- 
terposition of different substances between an excited 
electric and a body capable of being electrified by in- 
duction, occasions different degrees of excitement in 
the latter, even when the interposed bodies are glass, 
sulphur, and other “ non-conductors ;” and this he 
justly refers to a peculiar power or property of bodies 
called ‘‘specifie inductive capacity.” But this is 
rather different from the general proposition above 
referred to. 
‘ In conclusion of this part of the subject, I must 
ae add that Mr Faraday has, with great pains and suc- 
electricity cess, demonstrated the fundamentally identical nature 
from what- of electricity from whatever source derived, and how- 
eversource-ever differing in its usual manifestations ;—such as 
electricity of the pile, of the common machine, or that 
induced by magnetic, thermal, and animal electricity. 
These have all common properties, producing theshock, 
the spark, and magnetic, chemical, and heating effects; 
and, except two, also producing sensible attraction 
and repulsion, But the disproportion of the effects 
of electricity, varying so much in intensity when re- 
ferred to unit of quantity, is astonishing and para- 
doxical, The electricity which so silently and speedily 
decomposes a single grain of water would, when its 
intensity is sufficiently exalted, produce, according to 
Mr Faraday, “a very powerful flash of lightning,” 
or 800,000 times the contents of a well charged Ley- 
den battery. Again, zinc and platinum wires half an 
inch long and one-eighteenth inch diameter, dipped 
into slightly acidulated water, produce in three se- 
conds as much electricity as a man can easily bear 
in the form of a shock. 
(815.) 
(816.) II. Induction of electric currents from other cur- 
Indvetion ‘rents and from magnets.—This splendid research, 
electric 
currents— Which dates from 1831, constitutes the discovery of 
__-magneto- magneto-electricity. 
The discovery by Ampére of the attraction and 
repulsion of conductors conveying electric currents 
rapidly followed (as we have seen in Art, 796) Oer- 
ELECTRICITY.—DR FARADAY. 
979 
sted’s discovery of the power of electricity to affect 
the magnet, and the corollary from it of the mag- 
netizing agency of electricity. This being achieved, 
very striking analogies led to the expectations—1. 
That a wire conveying a current ought to excite by 
induction a current in another wire near it; and, 2. 
That a magnet ought, under some circumstances at 
least, to be capable of exciting electric action. But 
attempts in these directions had repeatedly and sig- 
nally failed, and for a reason which Mr Faraday first 
rendered apparent. 
Having made a compound helix of two copper _ (817.) 
wires wound parallel to one another, but not touch- ee 
ing, and rolled one within the other upon a cylin- tion, 
der, he found that when he transmitted a continu- 
ous voltaic current through one wire, a momen- 
tary current (tested by a galvanometer) took place 
in the independent helix in the same direction with 
the primary current; but it ceased to exist in- 
stantaneously, although the primary current conti- 
nued to act; and it was only on the cessation of 
that current that a new momentary induced current 
appeared, but in the contrary direction to the previ- 
ous one, The same effect occurred when a wire 
conducting a current was mechanically brought into 
the presence of another wire; the approximation of 
the two induced a similarly directed current, their 
separation a contrary effect. Whilst the wires were 
immovable no induced current took place. This 
he termed Volta-Electric Induction. 
Mr Faraday next took a ring of soft iron, disposing 
two copper-wire coils round opposite portions of the 
ring. In passing a current through one coil, and 
thus magnetizing the ring, a current was induced in 
the other copper coil, but, as in the former case, only 
for an instant. When the primary current stopped, 
and the magnet was wnmade, an opposite current 
shot through the secondary coil. 
The transition to the next experiment was natu- 819.) 
ral, but highly important. The primary coil was Magneto- 
suppressed ; and the piece Of soft iron embraced by “tricity: 
the secondary coil was now magnetized by the in- 
ductive action of a powerful bar magnet, with 
which contact was alternately made and broken. 
At the instant of making contact a momentary 
current of electricity was produced in the remain- 
ing coil, and on breaking it a reversed current, 
also of instantaneous duration. No current ex- 
isted whilst the magnet continued to be applied. 
The direction of the current at making contact 
was opposite to that which would have produced 
the magnetism present in the iron core; on break- 
ing contact the current was similar to that which 
would have magnetized the iron. ‘The electricity 
momentarily induced in the coil was tested by its 
action on the galvanometer, by its power to mag- 
netize steel, to convulse a frog, and finally by the 
(818.) 
1 Researches, Art, 504. 
