(792.) 
Speedily 
taken up 
by Am- 
pére, 
974 
nal, Oersted took no immediate measures either to 
complete or to publish his discovery. Some months 
appear to have elapsed whilst waiting for the conve- 
nience of a larger battery before he repeated the ex- 
periment with the aid of Professor Esmark and other 
friends. The battery then employed contained 20 
twelve-inch elements, charged with water and ,j,th of 
mixed nitrie and sulphuric acids. The conducting 
wire was heated red hot; which must have rather dimi- 
nished the effect than otherwise. The nature of the 
wire was found to be unimportant, If positive electri- 
city passed from north to south through a conducting 
wire placed horizontally in the magnetic meridian, 
then a compass needle suspended over it had its north 
end deviated to the west ; if under it, to the east; if 
the needle was placed on the east side of the conduc- 
tor, its north end was raised ; if on the wes¢ side, it 
was depressed. Oersted further found that needles 
of non-magnetic substances, such as brass and gum- 
lac, were not affected, and that the electrical efficiency 
depended on the quantity, not the intensity, of the 
current. These experiments seem to have been made 
in July 1820; and Oersted and his friends being now 
fully alive to the novelty and importance of the dis- 
covery, he circulated extensively copies of a Latin tract, 
dated the 21st July,in which the effects of the “electric 
conflict,” as he terms the presumed combination of the 
opposite electricities in the ‘‘ conjunctive wire’? upon 
a magnet, were described! In this tract we find the 
following expressions :—* The electric conflict acts 
in a revolving manner.” “It resembles a helix.” 
«The electric conflict is not confined to the conduct- 
ing wire, but it has around it a sphere of activity of 
considerable extent.” 
The effect of this pamphlet, consisting of a few 
pages only, was instantaneous and wonderful. The 
author probably counted on the opportunity of devel- 
oping his discovery at leisure, but it was seized on 
Arago, and with such avidity, and pursued with such signal suc- 
Davy. 
(798.) 
cess, particularly in France, that he probably gave up 
the race of invention in despair. Ampére had already 
communicated experiments to the Institute on the 
18th and 26th September. Arago and Davy sepa- 
rately, and but little later, discovered the magnetiz- 
ing power which the voltaic conductor exerted on iron 
filings, and the latter tried in vain the magnetizing 
power of common or machine electricity, which, how- 
ever, was soon after shown by Arago, who enclosed 
steel wires in helices of copper wire, through which 
the discharges were passed. When soft iron was 
placed in such a helix, it was found to become a tem- 
porary magnet of great power whilst the voltaic 
current continued, Thus magnets of enormously 
greater power than any previously known were con- 
structed ; one of the first large ones was made by Pro- 
fessor Henry of the United States. 
But the progress of electro- magnetismas a science 
MATHEMATICAL AND PHYSICAL SCIENCE. 
[Diss. VI. 
was far more indebted to Ampére, a professor at 
Paris, than to any other philosopher. I shall, 
therefore, introduce here some account of his dis- 
coveries before closing what I have to say of Oer- 
sted. 
Anpre Marre Ampere was born in 1775 at Lyon. 
(794.) 
He was an able mathematician, and wrote several Electro- 
memoirs on Chances, and on the Integration of Par- 
dynamic 
theory of 
tial Differential Equations. But with this he com- Ampere, 
bined a taste for, and a practical acquaintance with, 
the experimental sciences. He was a very good che- 
mist, and showed himself particularly attentive to 
Davy on his first visit to Paris. He was also much 
attached to metaphysical speculation. His skill in 
devising apparatus and in performing experiments was 
eminently shown in his electro-magnetic researches ; 
whilst he judiciously rendered his mathematical 
knowledge subservient to them. In this respect he 
had greatly the advantage of Oersted, who appears to 
have been little acquainted with mathematics, and, 
perhaps, in common with his metaphysical friends of 
the German school, misapprehended their utility in 
physical discoveries. Three different hypotheses 
Various 
were speedily broached to represent mechanically opinions 
the singular kind of force mutually exerted between 
a conductor and a magnet. 
on the 
ti 
The first and most ob- of SE akase 
vious was, that this action was not a push-and-pull tro-mag- 
force, but a force producing rotation without direct Bt force. 
attraction and repulsion, or of the nature of a couple 
exerted between any part of an electric current, and 
a small magnet or magnetic element. The second 
opinion was, that an electric current may be esteemed 
equivalent to a magnetizing force at right angles to 
it. The third, that a magnet is composed of ele- 
ments which act as if a closed electric circuit ex- 
isted independently within each of them ; that is, 
each magnetic molecule may be replaced by a small 
conducting wire bent upon itself, in which some un- 
failing source of electricity, like a galvanic pair, keeps 
up, in the same direction, a constant current. 
This last hypothesis, arbitrary and improbable as 
it may sound, was that defended by Ampére. Whilst 
few will be disposed to regard it as a true and com- 
plete physical picture of the condition of magnetized 
bodies, it seems impossible not to award to it the same 
sort of credit which we do to Newton’s “ fits of easy 
reflection and transmission” of light, when we find 
that it not only serves to represent the more obvious 
phenomena, but has suggested experiments absolutely 
new, and which turned out in accordance with the 
anticipation ; and that, finally, by the sagacity and 
industry of its author it was made to include, by 
merely mathematical deductions, and without any 
complication of the hypothesis, certain experiments 
of a very singular kind, which at first seemed inex- 
plicable by it. I proceed to develope a little farther 
this consideration. 
1 The exact title was, Lxperimenta circa efectum Conjflictus Electrici in Acum Magneticum. 
(795.) 
Theory or 
hypothesis 
adopted by 
Ampeére. 
