(801.) 
Seebeck. 
Discovery 
of thermo- 
electricity, 
(802.) 
Invention 
of the 
galvan- 
ometer— 
Schweig- 
ger and 
Nobili. 
(803.) 
Oersted’s 
history 
continued. 
976 
Whilst Ampére, Arago, Davy, the two De la 
Rives, and Mr Faraday, were throwing light on 
the causes, and developing the consequences of 
Oersted’s experiment, Seeseck of Berlin discovered 
in 1822 a new source of electric excitement, 
which has since become indirectly of very great im- 
portance. This was Thermo-Electricity. He found 
that when heterogeneous metals are united, either 
by soldering or pressure, and the junction heated, a 
current of electricity is established. The order of 
metals which produces the most energetic combina- 
tions, is wholly unlike the arrangement of the vol- 
taic series, and has no apparent reference to any 
other known property of those substances. Bismuth 
and antimony stand at the opposite extremities of 
the scale, and a pair formed of them is consequently 
the most powerful which can be made. When heat- 
ed at the junction, positive electricity passes from 
bismuth to antimony. In 1823, Oersted, then on 
a visit to Paris, united with Fourier in making 
experiments on this subject, and was probably the 
first who constructed thermo-electrical piles. Un- 
questionably, the most important application of these 
was to the construction of an instrument for measur- 
ing the effects of radiant heat, by Nobili and Melloni, 
of which an account has already been given, Art. 
(709). 
An application of electro-magnetism of extreme 
importance, was the Multiplier or Galvanometer, 
contrived by Schweigger of Halle. In it the idea 
was first realized of measuring the power of an 
electric current by its effect in deviating a mag- 
netic needle. Schweigger perceived that he could 
multiply the action of one and the same current, by 
causing it to traverse successive parallel coils of the 
conducting wire carried round the needle. Its sensibi- 
lity was still farther, and almost indefinitely increased 
by Nobili’s invention of rendering the needle astatic, or 
diminishing its natural directive power in anyrequired 
degree, This he did by connecting it firmly with a 
second needle parallel to the first, of nearly equal 
strength, with its poles placed in an inverted posi- 
tion relatively to the other, and moving freely in a 
plane altogether exterior to the coil, so that whilst 
the directive effect of the earth’s polarity is almost 
neutralized, the electro-magnetic effect of the coil 
tends to produce a similar deviation in both needles. 
This is one of the most precious philosophical instru- 
ments ever invented. It has been employed for 
thirty years in almost every electrical research or 
application. One of its best forms for many pur- 
poses (though hitherto little used) is the Torsion 
Galvanometer of Ritchie. 
Oersted, of course, interested himself in this new 
application of his own great discovery. Indeed, hav- 
ing the good fortune to survive that discovery for 
more than thirty years, with a full enjoyment 
of his intellectual vigour, he had the gratifica- 
tion of contemplating a body of science entirely 
MATHEMATICAL AND PHYSICAL SCIENCE. 
(Diss, VI. 
new as its results, and a variety of useful ap- 
plications scarcely Jess astonishing, which might, 
in one sense, be called his own creation. The dis- 
coveries of Ampére, Seebeck, and Mr Faraday, were 
all based upon his; and during those thirty years, this 
elegant and interesting branch of experimental phy- 
sics underwent an almost uninterrupted extension, 
such as hardly any other affords an example of. The 
Electric Telegraph is one of its most direct and practi- 
cal results ; nor should we omit that Oersted himself 
proposed, as far back as 1818, the application of elec- 
tricity to blasting rocks by the very same process in 
which it has of late years been so usefully applied, 
namely, that of heating a fine wire to incandescence, 
Though Oersted was the author of numerous 
papers connected with science down nearly to 
(804.) 
His experi- 
the close of his life, they do not contain any impor- ments on 
tant discovery, and with reference to electro-mag- 
netism, he appears to have contented himself princi- 
pally with repeating and expounding the observations 
of his contemporaries. But some of his experimentson 
other subjects deserve mention, especially those on the 
compressibility of water. This fact, which the Flo- 
rentine Academicians had vainly sought to establish 
in the 17th century, had been clearly demonstrated 
by Canton in the middle of the 18th, but Oersted 
first devised a compendious and effective apparatus 
for producing and measuring it more effectually. His 
result, that the compression amounts to 46-millionths 
‘of the bulk, for a pressure equal to one atmosphere, 
agrees almost precisely with Canton’s. In 1846, he 
considered that he had established that the heat de- 
veloped by the same amount of compression is -0203 
of a centigrade degree. He also made some experi- 
ments on the Law of the Compressibility of Air and 
upon other subjects. 
The desideratum of a clear expression of the mani- 
fest alliance between Electricity and Magnetism had 
been so long and so universally felt, that the discovery 
placed its author in the first rank of scientific men. 
There was not even, so far as I am aware, a sus- 
picion that he had been, however remotely or dimly, 
anticipated. The prize of the French Institute which 
had been awarded to Davy for his galvanic discoveries, 
was bestowed upon Oersted, and so far as I am inform- 
ed, has not been since adjudicated. Hewas elected first 
Correspondent, and finally Associate of the Academy 
of Sciences. He was personally known to many of 
the philosophers of Europe, having made repeated 
the com- 
pression of 
water, 
(805.) 
Oersted re- 
ceives the 
prize of 
the Insti- 
tute of 
France. 
journeys in France, Germany, and England. His His scien- 
agreeable manners and general information rendered tificcharac- 
him popular. Sir H. Davy, who visited him at Co- 
penhagen, describes him as. “ a man of simple man- 
ners, of no pretensions, and not of extensive re- 
sources.” Niebuhr, however, who viewed his cha- 
racter in a different light, says, ‘I scarcely know 
another natural philosopher with so much intellect, 
and freedom from prejudice and esprit de corps.” His 
writings were indeed too discursive, Professor Forch- 
ter, 
