486 MEMORIAL OF JOSEPH HENRY. 



battery and the kind of magnet in order to produce electro-magnetic 

 action at a distance : relations which Henry was the first to dis- 

 cover. This accomplishment justly entitles him to be regarded as 

 a man of genius and a discoverer of no mean order. This dis- 

 covery will always remain the one important fact that was to be 

 known, to be understood, and to be applied, before it was possible to 

 have constructed any form of electro-magnetic telegraph. 



Let us see how Henry made this discovery. After ending the 

 experiments with the one-cell battery and reaching results which 

 seemed to confirm the opinion of Barlow as to " the impracticability 

 of the scheme" of an electro-magnetic telegraph, Henry attached 

 his magnet to the second battery formed of 25 cells, arranged in 

 series. The current from this battery was sent to the magnet 

 through 1,060 feet of the same wire as had been used in the experi- 

 ments with the first battery of one cell. The magnet now lifted 

 eight ounces. It had held up only one ounce when with the same 

 length of interposed wire the battery of one cell was used. 



He now attached his electro-magnet directly to the poles of the 

 25-cell battery, when, to his astonishment, it only held 7 ounces. 

 The same magnet, it will be remembered, when attached to the one- 

 cell battery supported 72 ounces. 



Here were facts of the highest significance, and Henry was not 

 slow to seize them in all their bearings. Referring to these experi- 

 ments he says : " It is possible that the diiferent states of the trough, 

 with respect to dryness, may have exerted some influence on this 

 remarkable result; but that the effect of a current from a trough 

 (i. e. a series of cells) is at least not sensibly diminished by passing 

 through a long wire, is directly applicable to Mr. Barlow's project 

 of forming an electro-magnetic telegraph, and it is also of material 

 consequence in the construction of the galvanic coil." 



Henry speaking, in 1857, of these, his first gatherings into the 

 garner of science, says: "These steps in the advance of electro- 

 magnetism, though small, were such as to interest and astonish the 

 scientific world. With the same battery used by Mr. Sturgeon, at 

 least a hundred times more magnetism was produced than could 

 have been obtained by his experiment. These developments were 

 considered at the time of much importance in a scientific point of 



