Figure 47. — Henry's electromagnetic motor. From American Journal of Science, 



183 1, vol. 20, p. 342. 



square feet of zinc."* Two years later at Princeton 

 Henry devised an electromagnet that held the aston- 

 ishing weight of 3,600 pounds with a battery of 132 

 square inches of zinc that occupied only one cubic 

 foot. ''= 



In 1835 Professor Jacobi, apparently independent of 

 Henry, began a more complete and systematic inves- 

 tigation of the electromagnet.™ He completed this 

 study in 1844. " Henry's distinction between quantity 

 and intensity magnets was expressed again by Jacobi 

 when he asserted that the greatest magnetic force was 

 produced when the resistance of the coil equaled that 

 of the voltaic battery. By the time of Jacobi's experi- 

 mentation, several electric ixiotors had been con- 

 structed, and some of his results were summarized in 

 an article prescribing the proper design of a motor for 



'* Joseph Henry and Dr. Ten Eyck, "An Account of a Large 

 Electro-Magnet, Made for the Laboratory of Yale College," 

 American Journal of Science, 1831, vol. 20, pp. 201-203. 



'5 "Deposition of Joseph Henry, in the Case of Morse vs. 

 O'Reilly, taken at Boston, September, 1849," reprinted in 

 Annual Report of the . . . Smithsonian Institution . . . for ike Tear 

 1857, 1858, pp. 109-110. 



™ M. H. Jacobi, "On the Application of Electro-Magnetism 

 to the Moving of Machines," Sturgeon's Annals of Electricity, 

 1837, vol. 1, pp. 408-415, 419-444. 



" M. H. Jacobi and E. Lenz, "Ueber die Anziehung der 

 Elektromagnete," Annalen der Physik, 1839, vol. 47, pp. 401-418; 

 "Ueber die Gesetze der Elektromagnete," Annalen der Physik, 

 1839, vol. 47, pp. 225-270; 1844, vol. 61, pp. 254-280, 448-466, 

 and vol. 62, pp. 544-548. 



a boat.'* But we must turn back a little to examine 

 some of the steps that led to the development of the 

 motors of the 1840's. 



ELECTRIC MOTORS 



Once it was clear to Michael Faraday at the Royal 

 Institution in London that a current-carrying conduc- 

 tor exerted a force on a magnetic needle, he sought 

 some means of changing this static deflection into con- 

 tinuous rotation.'^ He finally succeeded in producing 

 the circulation of a wire about a magnet and the 

 circulation of a magnet about a wire (fig. 45). Peter 

 Barlow *° added some other devices to the ones Faraday 

 invented (fig. 46), but both Faraday's and Barlow's 

 apparatus were closer to "philosophical toys" than the 

 machine that Joseph Henry created in 1831,*' which 

 is illustrated in figure 47. 



Henry's apparatus was the first clear-cut instance 

 of a motor capable of further mechanical development. 



" M. H. Jacobi, "Ueber die Principien der elektromag- 

 netischen Maschinen," Annalen der Physik, 1840, vol. 51, pp. 

 358-372; "On the Principles of Electro-Magnetical Machines," 

 Sturgeon's Annals of Electricity, 1841, vol. 6, pp. 152-159. 



™ Michael Faraday, "On Some New Electro-Magnetical 

 Motions, and on the Theory of Magnetism," Qiiarterly Journal of 

 Science, Literature and Arts, 1822, vol. 12, pp. 74-96. 



s» Peter Barlow, "A Curious Electro-Magnetic Experiment,' 

 Philosophical Magazine, 1822, vol. 59, pp. 241-242. 



*' Joseph Henry, "On a Reciprocating Motion Produced by 

 Magnetic Attraction and Repulsion," American Journal of 

 Science, 1831, vol. 20, pp. 340-343. 



260 



BULLETIN 228 : CONTRIBUTIONS FROM THE MUSEUM OF HISTORY AND TECHNOLOGY 



