358 PIONEERS OF SCIENCE IN AMERICA. 



tery and the whole external resistance of the conjunctive wire 

 or conducting circuit ; with the very important practical con- 

 sequence that by combining with an ' intensity ' magnet of a 

 single extended fine coil an intensity battery of many small 

 pairs, its electro-motive force enables a very long conductor to 

 be employed with no sensible diminution of effect. ' It takes 

 nothing from Henry's discovery that Ohm had conceived a 

 mathematical theory of the same law in 1827. Except to a 

 few in Germany this theory was unknown, and did not affect 

 science in England, France, or America until much later. It 

 was unknown to Faraday and Wheatstone in 1837 ; to Bain in 



In 1831, Henry made an apparatus by which he caused a 

 steel bar, suspended between the poles of an electro.-magnet, 

 to swing and give signals by its strokes on a bell. He operated 

 this through more than a mile of wire. Here was a device 

 which might readily have been developed into an electric tele- 

 graph. 



Mr. Taylor says of this memorable arrangement : 



" In the first place, it was the first electro-magnetic tele- 

 graph employing an intensity magnet capable of being excited 

 at very great distances from a suitable intensity battery. . . . 



"In the second place, it was the first electro-magnetic 

 telegraph employing the armature as a signalling device ; or 

 employing the attractive power of the intermittent magnet as 

 distinguished from the directive action of the galvanic circuit ; 

 that is to say, it was, strictly speaking, the first magnetic tele- 

 graph. 



" In the third place, it was the first acoustic telegraph." 



This is the language of a eulogist, but it is a fact that 

 Morse did not succeed in making his telegraph operate through 

 any considerable length of wire until he adopted the intensity 

 magnet of Henry. To quote Henry's words in his Statement 

 in Relation to the History of the Electro-magnetic Telegraph, 

 published by the Regents of the Smithsonian Institution in 

 1857, "The principles I had developed were applied by Dr. 

 Gale to render Morse's machine effective at a distance." That 

 is Henry's connection with the Morse telegraph in a nut- 

 shell. 



The discoveries which he announced in 1831 attracted wide 

 attention among men of science, and were the cause of his 



