Henry, Joseph (1797-1878), the leading
American scientist after Benjamin Franklin until Willard Gibbs, was a professor at
Princeton from 1832 to 1846. His chief scientific contributions were in the field of
electromagnetism, where he discovered the phenomenon of self-inductance. The unit of
inductance, called ``the henry,'' immortalizes his name. Henry is also remembered as the
first Secretary of the Smithsonian Institution, where he made extraordinary contributions
to the organization and development of American science.
Of Scottish descent, Henry was the son of a day-laborer in Albany, N.Y. As a
small boy he was sent to live with his grandmother in a village about 40 miles from
Albany. There he worked in a general store after school hours and at the age of thirteen
was apprenticed to a watchmaker. As a young man he became interested in the theater and
was offered employment as a professional actor, but in 1819 several well-positioned Albany
friends persuaded him instead to attend the Albany Academy, where free tuition was
provided. His interest in science had already been aroused by a chance encounter with a
popular scientific book, and by 1823 his education was so far advanced that he was
assisting in the teaching of science courses. By 1826, after a stint as a district
schoolteacher and as a private tutor, he was appointed Professor of Mathematics and
Natural Philosophy at the Academy. Here, in spite of a teaching schedule that occupied him
seven hours a day, he did his most important scientific experiments.
Henry had become interested in terrestrial magnetism, which
was then, as today, an important scientific topic. This led him to experiment with
electromagnetism. His apprenticeship as a watchmaker stood him in good stead in the
construction of batteries and other apparatus. Oersted and others had observed magnetic
effects from electric currents, but Henry was the first to wind insulated wires around an
iron core to obtain powerful electromagnets. Before he left Albany, he built one for Yale
that would lift 2,300 pounds, the largest in the world at that time. In experimenting with
such magnets, Henry observed the large spark that was generated when the circuit was
broken, and he deduced the property known as self-inductance, the inertial characteristic
of an electric circuit. The self-inductance of a circuit tends to prevent the current from
changing; if a current is flowing, self-inductance tends to keep it flowing, or if an
electromotive force is applied self-inductance tends to keep it from building up. Henry
found that the self-inductance is greatly affected by the configuration of the circuit,
especially the coiling of the wire. He also discovered how to make non-inductive windings
by folding the wire back on itself.
While Henry was doing these experiments, Michael Faraday did
similar work in England. Henry was always slow in publishing his results, and he was
unaware of Faraday's work. Today Faraday is recognized as the discoverer of mutual
inductance (the basis of transformers), while Henry is credited with the discovery of
In 1832, when Henry was 35, Yale's distinguished geologist
Benjamin Silliman was consulted regarding the possible appointment of Henry to Princeton.
Silliman replied, ``As a physical philosopher he has no superior in our country; certainly
not among the young men.'' Henry, always modest, had responded to tentative inquiries,
``Are you aware of the fact that I am not a graduate of any college and that I am
Henry's initial salary at Princeton was $1,000 per annum plus
a house. The Trustees also provided $100 ``for the purchase of a new electrical machine
&c.'' At that point the College was near bankruptcy and Maclean was trying to
institute reforms and build up the faculty. Henry was a notable acquisition, and he found
the lighter teaching schedule and the intellectual companionship at Princeton congenial,
especially when his brother-in-law Stephen
Alexander joined the faculty to teach astronomy. Henry worked with Alexander in the
observation of sunspots and continued his own work on magnets, building for Princeton an
even larger magnet than he had built for Yale, one that would lift 3,500 pounds. He also
rigged two long wires, one in front of Nassau Hall and one behind, so that he was able to
send a signal by induction through the building. Another wire from his laboratory in
Philosophical Hall to his home on the campus (see Joseph Henry House) was used to send signals to his wife; this signal
system used a remote electromagnet to close a switch for a stronger local circuit, and
constituted in effect the invention of the magnetic relay. A similar arrangement was used
by S.F.B. Morse in the invention of the telegraph; Morse had consulted Henry and had used
one of his scientific papers. Later, Henry was called to testify in a patent suit
involving the telegraph, Morse vs. O'Reilly. Although Henry had encouraged and helped
Morse in his project, his testimony that the principle of the telegraph had been known to
himself and to Professor Wheatstone in England undermined Morse's claim to originality.
This led to much unpleasantness and controversy, but Henry's reputation emerged unscathed.
In addition to natural philosophy (physics), Henry taught
chemistry, geology, mineralogy, astronomy, and architecture -- in the words of Frederick
Seitz, Ph.D. '34, former president of the National Academy of Sciences, he was ``a very
large economy package.'' A rather reserved and quiet man, he was nevertheless a popular
teacher. The College gave Henry an opportunity, then unusual, to travel abroad on leave at
full salary. In 1837 he met Faraday, Wheatstone, and other British scientists, to whom he
explained his idea of ``quantity'' and ``intensity'' circuits (low and high impedance, in
modern terms). He returned to Princeton with a variety of scientific equipment purchased
During his remaining years in Princeton Henry continued his
electrical investigations, but also branched out into the study of phosphorescence, sound,
capillary action, and ballistics. In 1844 he was a member of a committee to investigate
the explosion of a gun during a demonstration on the new U.S.S. Princeton; the Secretaries
of State and Navy and several congressmen were among the spectators killed. His
experiments on gun castings on this committee led him into the subject of the molecular
cohesion of matter.
In 1846, having received from an Englishman, James Smithson,
a large bequest for the founding of an institution ``for the increase and diffusion of
knowledge among men,'' the U.S. Congress established the Smithsonian Institution. A
distinguished board was appointed, with instructions to find the best possible man to head
the new Institution as secretary, and the invitation was soon extended to Henry. He was
reluctant to leave Princeton and the opportunity to do his own scientific investigations.
``If I go,'' he said to a friend, ``I shall probably exchange permanent fame for transient
reputation.'' But he finally accepted and threw his enormous energy and knowledge and
experience into the development of the Smithsonian, which became the first great driving
force in the organization and direction of American science.
Henry was one of the original members of the National Academy
of Sciences and served as its second president. He was also a trustee of Princeton and
president of the American Association for the Advancement of Science. When he died in 1878
his funeral was attended by the president of the United States with his cabinet, the chief
justice and associate justices of the Supreme Court, by many members of both houses of
Congress, and by many scientists and other illustrious personages.
In 1872, John C. Green, founder of the School of Science at
Princeton, endowed a chair of physics in Henry's honor (held since then by C. F. Brackett,
W. F. Magie, E. P. Adams, H. D. Smyth, and J. A. Wheeler). Almost a century later, when
the main physics building, Jadwin Hall, was dedicated in 1970, the Physics Department
manifested its continuing esteem for Henry by declaring that all of the laboratory
facilities housed in Jadwin and Palmer Halls and the Elementary Particles Laboratory
should be collectively known as the Joseph Henry Laboratories. Some of Henry's laboratory
equipment is on display in the lobby of Jadwin Hall. His campus home, built to his design,
is called the Joseph
Henry House. In Washington his statue stands before the old Smithsonian Building.
Herbert S. Bailey, Jr.
From Alexander Leitch, A Princeton Companion, copyright
Princeton University Press (1978).
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