288 HENRY AND THE TELEGRAPH. 



K'ever let it be forgotten that he who first exalted the "qnaiitity" 

 magnet of Sturgeon from a power of twenty j^ounds to a power of twenty 

 hundred pounds, was the absolute creator of the " intensity " mag- 

 net; that magnet which alone is able to act at a great distance from its 

 exciting battery ; — that magnet which by very reason of its lower 

 " quantity " is alone applicable to the uses of telegraphy. 



As Professor Daniell has concisely stated the problem: "Electro- 

 magnets of the greatest power, even when the most energetic batteiies 

 are employed, utterly cease to act when they are connected by consider- 

 able lengths of wire with the battery."* 



Seven years after Henry's first experimental demonstration of this 

 unlooked-for result, and his comi)lete establishment of the conditions 

 required for magnetizing iron at great distances through very long con- 

 ducting wires. Prof. Charles Wheatstone, of King's College, London, 

 having found a difficulty in signaling through four miles of wii^e, was 

 enabled to work out the problem for his own telegraph, by help derived 

 from Henry's labors. And yet he permitted his colleague. Prof. John 

 P. Daniell, of King's College, to prefix to the passage above quoted 

 from the excellent treatise on " Chemical Philosophy," the remarkable 

 statement : " Ingenious as Professor Wheatstone's contrivances are, they 

 would have been of no avail for telegraphic purposes without the in- 

 vestigation, which he teas the first to malce, of the laws of electro-magnets, 

 when acted on through great lengths of wire." And this erroneous 

 declaration was published long after Henry's "quantity" and " intensity" 

 magnets had been employed in the experiments of European elec- 

 tricians ; and years after Professor Wheatstone himself had formed the 

 acquaintance of Henry, and in April, 1837, had learned from his own 

 lips an account of liis elaborate investigations and successful results.! 



Whether Baron Schilling ever experimented on a sufficient length of 

 circuit to encounter' the fundamental practical difficulty announced by 

 Barlow in 1825 does not appear ; but that formidable obstacle to the 

 axjtual extension of his enterprise, certainly existed until the year 1831, 

 when Henry announced that the principles demonstrated by his re- 

 searches in 1829 and 1830, were "directty applicable to the project of 

 forming an electro-magnetic telegraph." And while these principles 



(8vo. Niirnbcr<5 :) 1828, vol. xiv, pp. 475-493. Fourteen years after the publication of 

 the former memoir, this elaborate discussion was for the first time translated into 

 English, by Mr. William Francis. ("The Galvanic Circuit investigated mathemat>- 

 ically." Taylor's Scknllfic Memoirs, etc. London, 1841, vol. ii, pp. 401-506.) 



* Introduction to the Studij of Chemical rhilosophy, second c<^lition, 8vo. London, 

 1843, chap, xvi, sect. 859, p. 57"(). 



\ Smithsonian Report for 1.857, pp. Ill, 112. The following pertinent extract is 

 made from an excellent and appreciative memoir of the "Life and Work of Joseph 

 Henry," recently read at the annual session of the American Electrical Society, at 

 Chicago, HI., December 12, 1878, by one of its vice-presidents, Mr. Frank L. Poi)C : " In 

 185G, referring again to these experiments, Wheatstone writes : ' With this law and ita 

 applications, no persons in England, who had before occupied themselves with experi- 

 ments relating to electric telegraphs, had been acquainted.' ... It Avould seem 

 from the peculiar wording of Wheatst-oue's statement last quoted, that he must then 

 have been aware of Henry's priority in this res'pect, and had his experiments in mind, 

 at the time of writing it." (Journal of the Am. Electrical Societi/, vol. ii, pp. 135, 13(3.) 

 This subject is more fully considered iu the " Sui>i)lement," Note F. 



