ADDIJKSS OF I'KOF. A. 51. 5IAYER. 48] 



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he wound them with uncovered copper wire. The coils of the wir 

 were separated, so that the current flowed through the wire around 

 the surface of the iron. This magnet, in proportion to its weight, 

 was the most powerful made up to this date It certainly did not 

 require great mental effort or acumen on the part of .Sturgeon to 

 bend a straight bar magnet into the then common U form of the 

 permanent steel magnet known as the horse-shoe magnet; yet his 

 experiments with this magnet mark an important point of departure 

 in electric science, and evidently led Henry to his first and his most 

 important scientific research. 



I have now given as much of the history of electrical research as 

 is requisite to the understanding of Henry's position as a discoverer 

 in this branch of knowledge when, in 1827, he began to make 

 original experiments in electricity. 



As with many other men of originality, Henry's first essays were 

 in the direction of improving the means of illustrating well-estab- 

 lished scientific facts and principles. His first paper, of October, 

 1827, is interesting because it was his first. In it he improves on 

 the usual apparatus which had been used by Ampere and others to 

 show electro-dynamic actions, by employing several turns of insulated 

 wire instead of one, as had previously been the practice. Thus, for 

 example, to show the directive action of the earth's magnetism on a 

 freely-moving closed circuit, Henry covered copper wire with silk 

 and then made out of it a ring about 20 inches in diameter, formed 

 of several turns of tin' wire. Tin.' extremities of this wire were 

 soldered to zinc and copper plates. The coil was then suspended 

 bv silk filaments. On plunging the metal plates into a glass of 

 dilute acid the ring rotated around its point pf suspension till its 

 plain; took a permanent position at right angles to the magnetic 

 meridian. By a similar arrangement of two concentric coils, one 

 suspended within the other, he neatly showed the mutual actions of 

 voltaic currents (lowing in the same or in opposite directions ; which 

 facts are the foundations of Ampere's celebrated law. 



We now reach a period when Henry appears as a discoverer, and 



truly one of no mean order. As I remember his narration to me in 



the year 1859, it was as follow-: lie said that one evening he was 



sitting in his study in Albany with a friend, when, after a few 



:il 



