Professor Henry And His Philosophical Toys

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Five years later Henry, working part time and with inferior facilities, began to overtake his rival. To increase the power of his electromagnets Sturgeon had increased the size and power of his batteries. Henry had a more sophisticated goal: “The greatest magnetic force with the smallest quantity of galvanism.” He accomplished this by insulating the wire rather than the iron bar. At first he did this, or so the story goes, with white silk ribbons from his wife’s petticoats. By insulating the wire itself he was able to wind many turns around a horseshoe-shaped iron bar. (Sturgeon’s had carried but a single layer, as did the more powerful magnets of Gerard Moll of Holland.) Henry’s 1827 magnet with a single layer lifted fourteen pounds. With a second layer of insulated wire overlapping the lirst, it was able to lift twenty-eight pounds.

In much the same manner Henry built more powerful magnets, using larger iron bars and more turns of copper wire, ingeniously wound to create the greatest force. Sturgeon himself wrote that “Professor Henry has been able to produce a magnetic force which completely efli])ses every other in the whole annals of magnetism.” The Englishman’s crude device had become, in Henry’s hands, one of the wonders of the world- though the world might not have known about Henry’s work had not a publication of Moll’s spurred Henry into writing up his results for Benjamin Silliman’s American Journal of Science and Arts at Yale.

Henry built a magnet for Silliman that would lift 2,300 pounds. (Silliman noted proudly that this was eight times the lifting power of any European magnet.) He also constructed electromagnets for the Penfield Iron Works near Crown Point (later Port Henry), New York, where they were used to extract iron from pulverized ore. Here they caught the eye of an itinerant blacksmith, Thomas Davenport, who later used them in his invention of the rotary motor.

It was Henry, however, who assembled what was probably the world’s first electromagnetic motor, using, as Henry put it in Silliman’s Journal of July, 1831, “a power which I believe has never before been applied in mechanics … magnetic attraction and repulsion.” The design of Henry’s simple device was reminiscent of the “rocker” steam engines of Thomas Newcomen and James Watt. The motor worked very well, but Henry compared the efficiency of the galvanic battery, its power source, with that of coal and noted that it came in a poor second best. “In its present state,” Henry wrote, “[the motor] can only be considered a philosophical toy.” But he had the foresight to add: “… it is not impossible that the same principle … may hereafter be applied to some useful purpose.”

In the meantime Henry had been working on a device from which he expected more immediate and practical results, the electromagnetic telegraph. The telegraph itself was nothing new at the time. Lesage had built one as early as 1774 in Geneva, and in 1798 the Spaniard Francisco Salva communicated over the twenty-six-mile span between Madrid and Aranjuez. But these instruments were not electromagnetic, and they did not have an audible signal. They were powered by the old electrostatic machines originally devised by Otto von Guericke and later used by Franklin and his contemporaries. A charge of static electricity would be built up on the machines, spark up the line, and be observed at the receiving end by the action of pith balls or the leaves of an electroscope-laboratory devices known to everyone who has taken high-school physics.

This was what we now call high voltage, low am. perage current (at the time the volt and the ampere had yet to be defined), and it passed through long wires without any significant diminution. The original voltaic batteries, however, produced high amperage and low voltage. André Ampère was one of the first to suggest that a current passing through a line might serve to transmit a signal, since an observer on the receiving end could note the deflection of a magnetic needle; but he offered no solution as to how this might be done using the ordinary battery as a power source. The problem was pursued further by Peter Barlow, an English mathematics teacher, in 1825, but Barlow found a significant decrease in the strength of his electromagnetic current at a distance of only two hundred feet from his battery. He gloomily concluded that the scheme was totally impractical.

Henry began his work on the telegraph in 1830. Aided by an assistant, he strung 1,060 feet of wire around the lecture room of the Albany Academy and installed an electromagnet at one end, a battery at the other. After several experiments he succeeded in lifting an eight-ounce weight with the electromagnet. Henry observed: “The fact that a magnetic action of a current from a trough is, at least , not sensibly diminished by passing through a long wire, is directly applicable to Mr. Barlow’s project of forming an electromagnetic telegraph …”