of a route
for a State road, three hundred miles long, between the Hudson River and
Lake Erie. The experience he gained in this work changed the course
of his career; he decided to follow civil and mechanical engineering
instead of medicine. Then in 1826 he became teacher of mathematics and
natural philosophy in the Albany Academy.

It was in the Albany Academy that he began that wide series of
experiments and investigations which touched so many phases of the great
problem of electricity. His first discovery was that a magnet could be
immensely strengthened by winding it with insulated wire. He was the
first to employ insulated wire wound as on a spool and was able finally
to make a magnet which would lift thirty-five hundred pounds. 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.

The attempt to send signals by electricity had been made many times
before Henry became interested in the problem. On the invention of
Sturgeon's magnet there had been hopes in England of a successful
solution, but in the experiments that followed the current became
so weak after a few hundred feet that the idea was pronounced
impracticable. Henry strung a mile of fine wire in the Academy, placed
an "int