. Bulletin. Science. Figure 49.—Ritchie's motor. From Philosophi- cal Transactions oj the Royal Society oj London, 1833, vol. 123, p. 316, pi. 7. polarization and secondary action, as was true of all its predecessors. Beginning in the middle 1830's chemical cells were being invented that avoided the polarization and local action of earlier cells. These new cells were good sources of current, and they could produce this current over a longer period of time than could the earlier cells. In addition scientists understood better how to build a strong electromagnet, and how to turn its force on and
. Bulletin. Science. Figure 49.—Ritchie's motor. From Philosophi- cal Transactions oj the Royal Society oj London, 1833, vol. 123, p. 316, pi. 7. polarization and secondary action, as was true of all its predecessors. Beginning in the middle 1830's chemical cells were being invented that avoided the polarization and local action of earlier cells. These new cells were good sources of current, and they could produce this current over a longer period of time than could the earlier cells. In addition scientists understood better how to build a strong electromagnet, and how to turn its force on and off by a commutator. It was no accident that electric motors began to seem prac- tical to inventors in the 1830's, for the main elements of a motor were present; it was not long before inventors began to assemble these elements into a device that could be used to drive machinery. In 1836 William Sturgeon ^^ asserted that he had constructed an electric motor in the fall of 1832 (fig. 51), had demonstrated it in March 1833, and had later used it to run models of machinery. Francis Watkins *^ made electric motors (fig. 52) in 1835 that could also be used to drive mechanical models. In May 1834 M. H. Jacobi'* built an electric motor (fig. 53) that could lift 10 to 12 pounds at a speed of one foot per second when tested by a Prony brake. Further details on this motor, showing how much zinc was needed to produce a given amount of mechanical work, appeared the following year.*^ Jacobi claimed that a half-pound of zinc would deliver the "demi-force d'un homme" for 8 hours. S9 William Sturgeon, "Description of an Electro-Magnetic Engine for Turning Machinery," Sturgeon's Annals of Electricity, 1836, vol. 1, pp. 75-78. " Francis Watkins, "On Magneto-Electric Induction," Philosophical Magazine, 1835, vol. 7, pp. 107-113; "On Electro- Magnetic Motive Machines," Philosophical Magazine, ser. 3, 1838, vol. 12, pp. 190-196. 88 M. H. Jacobi in Vln
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