The Three Secretaries 125 



"But in addition to this large gift to science, Henry (as 

 we have seen) has the preeminent claim to popular gratitude 

 of having first practically worked out the differing functions 

 of two entirely different kinds of electro-magnet : the one 

 surrounded with numerous coils of no great length, desig- 

 nated by him the ' quantity' magnet, the other surrounded 

 with a continuous coil of very great length, designated by 

 him the ' intensity ' magnet. The latter and feebler system 

 (requiring for its action a battery of numerous elements,) 

 was shown to have the singular capability (never before 

 suspected or imagined) of subtle excitation from a distant 

 source. Here for the first time is experimentally established 

 the important principle that there must be a proportion be- 

 tween the aggregate internal resistance of the battery and 

 the whole external resistance of the conjunctive wire or con- 

 ducting circuit. This was a very important though uncon- 

 scious experimental confirmation of the mathematical theory 

 of Ohm, embodied in his formula expressing the relation be- 

 tween electric flow and electric resistance, which, though pro- 

 pounded two or three years previously, failed for a long time 

 to attract any attention from the scientific world. 



" Never should it be forgotten that he who exalted the 

 'quantity' magnet of Sturgeon from a power of twenty pounds 

 to a power of twenty hundred pounds, was the absolute CREA- 

 TOR of the 'intensity' magnet; and that the principles in- 

 volved in this creation, constitute the indispensable basis of 

 every form of the electro-magnetic telegraph since invented." 3 



The first labor in which this infant giant was employed 

 was to demonstrate the practicability of the telegraph. By 

 its aid Henry was enabled in 1829 or 1830 to pass a current 

 through a wire 1060 feet in length and to lift at its end a 

 considerable weight. 



"This was the first discovery of the fact that a galvanic 

 current could be transmitted to a great distance with so little 

 diminution of force as to produce mechanical effects." So 

 said Henry in 1857, critically reviewing the progress of elec- 



1 Taylor, William B. "Memorial of Joseph Henry," page 226. 



