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Figure 45. — A model of Faraday's circulating 

 wire experiment. {USNM 31^046; Smithsonian 

 photo 4J048-C.) 



There were some experimenters in the United 

 States, like James Dana and Rubens Peak, who were 

 also exhibiting electromagnets about this time. A 

 more serious investigator was Joseph Henry, then an 

 instructor at Albany [New York] Academy but who 

 was to become the first Secretary of the Smithsonian 

 Institution. He was one of the first to try to obtain the 

 optimum electromagnet from a given battery. Like 

 Poggendorff, '^ Henry found that the pull of an electro- 

 magnet could be increased by adding more turns of 

 wire but only up to a certain number of turns. After 

 that number was reached, in order to increase the 

 force, either the additional turns had to be connected 

 in parallel with the turns already on the coil or a bat- 



Figure 46. — Barlow's wheel. From Philosophical 

 Magazine, 1822, vol. 59, pi. 4, fig. 4. 



tery with more pairs of plates had to be utilized. 

 These considerations led Henry to distinguish the kind 

 of battery to which each of two kinds of electromagnets 

 responded best: a quantity electromagnet of coils 

 of wire in parallel that responded best to a quantity 

 battery like Hare's calorimotor where the area of the 

 plates is large, and an intensity electromagnet that 

 responded best to an intensity battery like the 

 Cruickshank trough where the number of plates is 

 large. A quantity electromagnet and battery were 

 the best to use for maximum lifting power; while to 

 operate an electromagnet at the end of a long line 

 of wire, an intensity battery at one end and an 

 intensity electromagnet at the other were necessary. 

 On the basis of such considerations, Henry con- 

 structed a quantity electromagnet (fig. 43) with a 

 core weighing 21 pounds that used a cell with 72 

 square inches of zinc to lift 750 pounds.'^ When 

 Professor Silliman of Yale heard of this feat, he re- 

 quested Henry to make an even larger magnet, and 

 in 1831 Henry constructed a magnet (fig. 44) weighing 

 59 pounds that lifted 2,000 pounds with a cell using 5 



'-J. C. Poggendorff, "Physisch-chemische Untersuchungen 

 zur nahern Kenntnis des Magnetismus der voltaischen Saule," 

 Oken's Isis, 1821, vol. 1, cols. 687-710. 



" Joseph Henry, "On the Application of the Principle of the 

 Galvanic Multiplier to Electro-Magnetic Apparatus, and 

 also to the Development of Great Magnetic Power in Soft Iron, 

 with a Small Galvanic Element," American Journal of Science, 

 1831, vol. 19, pp. 400-408. 



PAPER 28: DEVELOPMENT OF ELECTRICAL TECHNOLOGY IN THE 19TH CENTURY: I 



259 



