![]() ![]() 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. The challenge in developing a motor was to use a battery current to produce not only a mechanical effect, but continuous mechanical movement. These basic discoveries led him to develop both a motor and a bell-ringing device that was a precursor to Morse's electromagnetic telegraph. 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. Henry detailed his research and findings in letters to colleagues, including Benjamin Silliman, Sr. 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. 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). This was unknowingly a demonstration of Ohm's Law which had been published in 1826, but was not yet widely known or understood. 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). 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 parallel -an alternative arrangement was to have larger plates in a single battery) to increase the quantity (current). 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. 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. The field of electromagnetism was only six years old when Henry began teaching at the Albany Academy in New York. ![]() 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. Although he did not further develop these devices, his work paved the way for the development of motors by others and for Samuel F. 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. 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. During these years, he became known among scientists throughout the United States and Europe for his groundbreaking research in electromagnetism. Henry was a physicist who had taught for some twenty years, first at a college preparatory school in New York and then at Princeton. 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. ![]()
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