ensity" battery at one end, and made the armature strike a bell
at the other. Thus he discovered the essential principle of the electric
telegraph. This discovery was made in 1831, the year before the idea of
a working electric telegraph flashed on the mind of Morse. There was no
occasion for the controversy which took place later as to who invented
the telegraph. That was Morse's achievement, but the discovery of the
great fact, which startled Morse into activity, was Henry's achievement.
In Henry's own words: "This was the first discovery of the fact that a
galvanic current could be transmitted to a great distance with so little
a diminution of force as to produce mechanical effects, and of the means
by which the transmission could be accomplished. I saw that the electric
telegraph was now practicable." He says further, however: "I had not in
mind any particular form of telegraph, but referred only to the general
fact that it was now demonstrated that a galvanic current could be
transmitted to great distances, with sufficient power to produce
mechanical effects adequate to the desired object."*

* Deposition of Joseph Henry, September 7, 1849, printed in
Morse, "The Electra-Magnetic Telegraph", p. 91.

Henry next turned to the possibility of a magnetic engine for the
production of power and succeeded in making a reciprocating-bar motor,
on which he installed the first automatic pole changer, or commutator,
ever used with an electric battery. He did not succeed in producing
direct rotary motion. His bar oscillated like the walking beam of a
steamboat.

Henry was appointed in 1839. Professor of Natural Philosophy in the
College of New Jersey, better known today as Princeton University. There
he repeated his old experiments on a larger scale, confirmed Steinheil's
experiment of using the earth as return conductor, showed how a feeble
current would be strengthened, and how a small magnet could be used as
a circuit maker and breaker. Here were the principles of the telegraph
relay and the dynamo.

Why, then, if the work of Henry was so important, is his name almost
forgotten, except by men of science, and not given to any one of the
practical applications of electricity? The answer is plain. Henry was an
investigator, not an inventor. He states his position very clearly: "I
never myself attempted to reduce the principles to practice, or to
apply any of my discoveries to processes in the arts. My whole
atten