Evening star. [volume] (Washington, D.C.) 1854-1972, 1882-08-12
Terrestrial yTa.netism

Ersted, very early in the present century.
discovered by accident the power exercised by a
current on magnet in its neighborhood. He
was holding the mariners compass in his hand,
and accidentally approached it to wire through
which current was passing. By brilliant
effort of inductive reasoning he at once came to
the conclusion that the magnet was DETECTED in
consequence of the nearness of the current
overcoming for the moment the directing force
of the earth's magnetism and it flashed across
his mind that the reason why the magnet itself
points to the north was owing to the directing
force OF currents passing east and west round
the earth. The idea. thus started. deyel-
Oped into electromagnetic. The theory
OF Ersted was confirmed in a remarkable man.
ner by an experiment devised by Prof. Barlow
believe it is not SO generally known as its inpe-
nuity and Importance deserve. He wound
copper spiral wire round ahollow globe of wood
in such manner as to make the coils coincide
with the parallels of latitude. He then covered
the sphere and its spiral wire with the pictured
cores OF a terrestrial globe in such way as to
bring the poles of the electromagnetic spiral into
the same position as the observed magnetic
poles. The globe thus arranged was then
placed under delicatey suspended needle.
and electromagnetic currents were caused to
circulate in the spiral wire beneath the surface
The needle so suspended exhibited under the
influence OF the spiral currents, all the phe-
nomena OF variation exhibited by the COM
pass needle on the actual globe | think the
story is told in Sir William Snow Harris
Magnetism" 1t sufficiently establishes the
accuracy of the opinion that the movements
of the compass needle are due to currents of
terrestrial magnetism. The point is one of
extreme Importance, because it led Arago to
observe shortly afterward that a current sur
rounding O bar of soft iron would magnetic the
bar; and Faraday drew the further conclusion
that the converse was also true. and that a
magnet would produce a current If presented
to closed spiral circuit The theoretical in
ference drawn by Faraday was afterward
proved by actual experiment to be a fact
Subsequent steps in electro magnetism were
after these discoveries, mere questions of time
and patience; and it was matter of detail to
discover the means by which such currents
might be collected. intensified, and utilized.
Such. then. was the condition of electrical
science. when, couple of years age. circum-
stances turned the attention of the whole BODY
of inventors to electromagnetic. No posi-
tiveiy new discovery was made: all the princ-
pies involved in the elaborate systems of cleo
trio lighting which has lately attracted SO much
attention had already been made known by
Faraday. aid Gramme following in the foot
steps of PacinOtti, had constructed machines
which are in every essential particular the same
. as the dynamO-electric machines of to-day but
|. though the principle was established, and the
machines of dramme, Ladd Siemens. and MANY
Others were in occasional use. and were indeed
somewhat extensively employed in physical
iduoLd.otitS duu IoI HeuiCai purpOSeS,Cll atten-
ton of electricians seemedt to be mainly concen-
trated on devising Improvements in voltaic cleo
tricity. But a great change suddenly Oc-
cured. Chemical electricity supplies
current, highly manageable and use
full, but not of sufficient strength to
perform rough work or efficiently maintain
the electric light. Perhaps it would be more
accurate to say that zinc is SO expensive that
the production of current by m, ans of zinc
combustion sufficiently powerful to perform
heavy work was economically impossible, and
practically was not attempted. But the pro-
blem of utilizing electricity in the everyday
requirements of life as a motive power and as
a source of light. has how every chance of being
solved. Engines moved by electricity are con-
structed, and light, brilliant and beautiful, is pro-
duced in abundance. What remains is mere
question OF COST and the ingenuity of thous-
and workers is busily employed in reducing that
to minimum. little while ago it seemed as
if voltac electricity would be retained at least
for telegraphic purposes. for which it seemed to
be specially adapted; but even in this respect it
is doubtful whether it will not be superseded.
Already some of the principal American tele-
graph lines employ dynamic instead of voltaic
batteries for their daily work; and it seems
probable that, in combination with some form
of storage Cot which Pante Faure and Sellon
have shown the possibility. electro-m magnetism
will carry all before it.-TiScount Burr in the
Nineteeufh (e1tlt,-u