Electromagnetism

Joseph Henry, by Unknown, 1860, Smithsonian Archives - History Div, SIA2012-7648 or 82-3172.

 

Joseph Henry, who became Secretary of the Smithsonian upon its establishment in 1846, was the first in a long line of scientists selected to lead the Institution. Henry was a physicist who had taught for some twenty years, first at a college preparatory school in New York and then at Princeton. During these years, he became known among scientists throughout the United States and Europe for his groundbreaking research in electromagnetism.

EXPERIMENTING IN ELECTROMAGNETISM

Henry was an innovative teacher whose interest in the relatively new field of electromagnetism, combined with his belief in the importance of demonstrating scientific phenomena to his students, led him to develop electromagnets that were far more powerful than any previously made. Using these electromagnets to demonstrate both dramatic and subtle effects to his students and to explore electromagnetism in the laboratory, he developed the first motor based on magnetic attraction and repulsion (a forerunner of a modern DC or direct current motor) and a primitive form of the electromagnetic telegraph. Although he did not further develop these devices, his work paved the way for the development of motors by others and for Samuel F. B. Morse's telegraph. He also discovered important principles of electromagnetic induction, for which he was honored in 1893, when the International Congress of Electricians named the unit of induction the "henry." Henry's work in electromagnetism not only made important contributions to science, but helped lay the groundwork for modern industry and telecommunications.

Albany Academy Where Joseph Henry Taught, by Unknown, Unknown, Smithsonian Archives - History Div, 96-4474.The field of electromagnetism was only six years old when Henry began teaching at the Albany Academy in New York. Danish scientist Hans Christian Oersted had discovered in 1820 that an electrical current in a wire from a battery caused a nearby compass needle to deflect. Eager to demonstrate electromagnetic phenomena to his students, Henry built upon the work of English scientist William Sturgeon, who in 1825 discovered that wrapping a wire around an iron core enhanced the magnetic effect. Henry experimented with various parameters: insulating the wire so that multiple layers could be wound on the core (Sturgeon had used bare wire with a layer of insulating shellac on the iron); winding several coils on the same core; connecting batteries end-to-end (in series) to increase the intensity (voltage) and side-by side (in parallelan alternative arrangement was to have larger plates in a single battery) to increase the quantity (current). He found that a high-intensity source worked best with the coils connected to end-to-end (in series, making a single coil), while a high quantity source was better with the coil ends connected together (in parallel). This was unknowingly a demonstration of Ohm's Law which had been published in 1826, but was not yet widely known or understood. By 1831, he reported making an electromagnet that could lift 750 pounds, over thirty-five times its own weight (with coils in parallel, using a quantity battery).1 Henry later remarked that these early electromagnets "possessed magnetic power superior to that of any before known."2 By 1833, he had built one that could lift over 3,300 pounds. Henry detailed his research and findings in letters to colleagues, including Benjamin Silliman, Sr. (1830), (1831), John Henry (1831), Edward Hitchcock (1832), and Parker Cleaveland (1831), (1832).

DISCOVERIES IN ELECTROMAGNETISM

In working to make more efficient use of his batteries and maximize the power of his electromagnets, Henry made basic discoveries in electromagnetism, including what specific types of electrical input should be matched to what types of circuits depending on the effects desired. These basic discoveries led him to develop both a motor and a bell-ringing device that was a precursor to Morse's electromagnetic telegraph. The challenge in developing a motor was to use a battery current to produce not only a mechanical effect, but continuous mechanical movement. Henry's reciprocating motor consisted of a straight electromagnet balanced on an axis with its ends above the north poles of two vertical permanent magnets. Pairs of wires, attached to each end of the electromagnet, alternately dipped into cups of mercury, acting as terminals of an electrochemical cell. As the wires alternately moved into and out of the cups, thus making and breaking a circuit, the polarity of the electromagnet was repeatedly reversed, which produced a continuous rocking motion. Henry was able to achieve "uniform motion, at the rate of seventy-five vibrations in a minute . . . for more than an hour."3 Although Henry's device contained the elements of a modern DC motor, Henry saw it primarily as a "philosophical toy" for classroom demonstrations, and did not attempt to patent it. In reference to the magnet's back-and-forth motion, Henry referred to this device as his "sheeps tail."

THE ELECTROMAGNETIC TELEGRAPH

Electromagnet Made by Joseph Henry, by Unknown, 1978, Smithsonian Archives - History Div, 78-6063.The challenge in devising an electromagnetic telegraph was not to produce continuous motion, but rather mechanical action at a great distance from a battery. Prior to Henry's research, electrical signals could not be sent through long wires. English scientist Peter Barlow, had, in fact, speculated that the inability to transmit a signal over more than two hundred feet meant that an electromagnetic telegraph was not possible. In varying parameters while developing his powerful electromagnets, Henry had discovered that while a single pair of plates was best to send a current through several shorter wires, a trough battery of multiple plates (high intensity) could send a current through a very long wire. The use of a high-intensity battery with a multiple-winding coil was essential to the development of the electromagnetic telegraph, since the losses in a long line would be relatively small. Morse learned this (indirectly from Henry) in 1837, with dramatic consequences. Evidence of Henry's foundational research on the electromagnetic telegraph dates to 1830, when he first began demonstrating to his students in Albany that a battery current could be transmitted through a thousand-foot wire. At the far end of the wire, an energized electromagnet attracted one end of a bar magnet suspended on a pivot, which caused the other end to strike a bell. One of Henry's Albany Academy students reported seeing Henry succeed with a circuit one-and-a-half miles long.4

Henry continued to develop more powerful electromagnets and demonstrated to his students a way in which mechanical effects could be produced at a much longer range than previously realized. Henry used a small "intensity" magnet in a local circuit to control a large "quantity" magnet holding up hundreds of pounds of weights. When he energized the small magnet through a long circuit, it attracted upwards a piece of wire, which broke the local circuit and caused the weights to fall with a crash. He did not publish a description of this primitive relay, which Morse learned of through an intermediary and which was critical in Morse's development of the telegraph, but mentioned it to Charles Wheatstone in England in 1837 and claimed to have demonstrated it to his Princeton students several years earlier. Although Henry had no interest in pursuing commercial applications, he would later point to these demonstrations as the first to show that an electromagnetic telegraph was possible.5

Morse's Experimental Telegraph, by Unknown, Date unknown, c. 1920s?, Smithsonian Archives - History Div, 91-3689.While Samuel Morse was developing his telegraph, he sought advice and public support from Joseph Henry. In a letter that would later be cited to establish the telegraph's origin, Henry wrote to Morse in 1842 that although such an invention had been suggested "by various persons from the time of Franklin to the present," it was not "until within the last few years or since the discoveries in electro-magnetism" that it had been practicable. Henry went on to say that "little credit can be claimed" for the telegraph's invention "since it is one which would naturally arise in the mind of almost any person familiar with the phenomena of electricity," but he supported Morse's design over the needle telegraphs being proposed by European scientists. Three years later, the publication of a book on the telegraph by one of Morse's chief assistants, Alfred Vail, failed to credit Henry's contributions and marked the beginning of a dispute between Henry and Morse6 that lasted many years.

ELECTROMAGNETISM RESEARCH

Michael Faraday, by Unknown, c. 1830s, Smithsonian Archives - History Div, SIA2012-1087 and SA-523.Henry's work with his powerful and versatile electromagnets, his motors, and telegraph circuits led him to complete important research in electromagnetism. In the years since Oersted had reported producing a magnetic effect from a battery current, scientists had tried to produce the complementary effect: the production of electricity from magnetism. Working in England, Michael Faraday was the first to report success in November 1831. Although Henry had begun work in this area in August 1831, at about the same time as Faraday, he encountered obstacles and delays throughout the academic year and did not begin working in earnest until June 1832. Faraday is thus credited with first achieving the effect, later termed mutual induction. Henry's biographer, Albert Moyer, makes a compelling case, however, that Faraday was both inspired to undertake his research after reading of possible implications of Henry's work with his electromagnets and was helped considerably by learning of Henry's powerful electromagnets and his use of multiple coils.7

Although Henry's report on inducing electricity from magnetism followed Faraday's, his investigation of the sparks he had observed when his reciprocating motor repeatedly made and broke a circuit, and those he had noticed when experimenting with the long wires he used in his telegraph experiments, led to his discovery, announced in July 1832, of what is known as self-induction.8 Self-induction occurs when a break in a circuit causes a waning magnetic field, which induces a momentary current in the original circuit in a direction opposite to that of the original current. For his independent discovery of mutual induction, and for being the first to discover self-induction, Moyer credits Henry with "not only a foundational concept in the physics of electricity and magnetism but also the much acclaimed principle behind the technology of electrical transformers and generators—two mainstays of modern industrialization."9

ELECTROMAGNETIC LEGACY

While Joseph Henry was required to put much of his own research aside once he came to Washington, DC, in 1846, his career as a physicist had a profound impact on his leadership of the Smithsonian. Henry's top priority was to support basic research, and his dedication to this vision throughout his secretaryship brought the Institution worldwide respect.

 

FURTHER RESOURCES

Roger Sherman, "Joseph Henry’s Contributions to the Electromagnet and the Electric Motor," Smithsonian Institution.

David Hochfelder, "Joseph Henry: Inventor of the Telegraph?," Smithsonian Institution Archives.

Frank Rives Millikan, "Joseph Henry: Father of the Weather Service," Smithsonian Institution Archives.

Courtney Esposito, "A Forgotten History: Alfred Vail and Samuel Morse," The Bigger Picture (blog), Smithsonian Institution Archives, May 24, 2011.

 

FOOTNOTES

1 Henry constructed this magnet based on principles outlined in a paper published in Silliman's American Journal of Science 19 (January 1831): 400–408. The magnet was described in Silliman's American Journal of Science 20 (April 1831): 201–208. Return to text

2 Joseph Henry, "Communication from Prof. Henry, Secretary of the Smithsonian Institution, Relative to a Publication by Prof. Morse," Annual Report of the Board of Regents of the Smithsonian Institution for the Year 1857, (Washington, DC: US Government Printing Office, 1858), 109. Return to text

3 Henry announced his motor in the article, "On a Reciprocating Motion Produced by Attraction and Repulsion," Silliman’s Journal of American Science 20 (1831): 340–348. Return to text

4 Albert E. Moyer, Joseph Henry: The Rise of an American Scientist (Washington, DC: Smithsonian Institution Press, 1997), 65–69. Return to text

5 Joseph Henry, "Statement of Professor Henry in Relation to the History of the Electro-Magnetic Telegraph," appendix to Annual Report of the Board of Regents of the Smithsonian Institution for the Year 1857, (Washington, DC: US Government Printing Office, 1858), 99. Return to text

6 Marc Rothenberg, Kathleen Dorman, John C. Rumm, and Paul Theerman eds., The Princeton Years: January 1844–December 1846, vol. 6 of The Papers of Joseph Henry, (Washington, DC: Smithsonian Institution, 1992), 326n–327n. Return to text

7 Moyer, Joseph Henry: The Rise of an American Scientist, 79–86. Return to text

8 Silliman’s Journal of American Science 22 (July 1832): 143-155. Henry announced his discovery of self-induction in the same article, "On a disturbance of the Earth’s magnetism, in connexion with the appearance of an Aurora Borealis, as observed at Albany, April 19, 1831," as he announced his discovery of mutual induction; Nathan Reingold, Arthur P. Molella, and Michele L. Aldrich, eds., The Princeton Years: November 1832-December 1853, vol. 2 of The Papers of Joseph Henry (Washington, DC: Smithsonian Institution Press, 1975), 329n. Return to text

9 Moyer, Joseph Henry: The Rise of an American Scientist, 80. For Henry's five-part series to the American Philosophical Society on his electromagnetic research, entitled "Contributions to Electricity and Magnetism," see Contributions I, Contributions II, Contributions III   , Contributions IV, Contributions V. Return to text