He first showed the difference
between "quantity" magnets composed of short lengths of wire
connected in parallel, excited by a few large cells, and
"intensity" magnets wound with a single long wire and excited by
a battery composed of cells in series. This was an original
discovery, greatly increasing both the immediate usefulness of
the magnet and its possibilities for future experiments.
The learned men of Europe, Faraday, Sturgeon, and the rest, were
quick to recognize the value of the discoveries of the young
Albany schoolmaster. Sturgeon magnanimously said: "Professor
Henry has been enabled to produce a magnetic force which totally
eclipses every other in the whole annals of magnetism; and no
parallel is to be found since the miraculous suspension of the
celebrated Oriental imposter in his iron coffin."*
* Philosophical Magazine, vol. XI, p. 199 (March, 1832).
Henry also discovered the phenomena of self induction and mutual
induction. A current sent through a wire in the second story of
the building induced currents through a similar wire in the
cellar two floors below. In this discovery Henry anticipated
Faraday though his results as to mutual induction were not
published until he had heard rumors of Faraday's discovery, which
he thought to be something different.
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