JOSEPH HENRY. 



attain the result had for six years failed to make such an ex- 

 tension. Nor was the result by any means made antecedently 

 assured by Schweigger's success with the galvanometer. If 

 Sturgeon's improvement of economizing the battery size and 

 consumption by increasing the magnet factor (in those few 

 cases where available) was well deserving of reward,* surely 

 Henry's improvement of a far greater economy, by increasing 

 the circuit factor (entirely neglected by Sturgeon), deserved 

 a still higher applause." 



In describing Henry's work during the next few years Mr. 

 Taylor continues: " To Henry belongs the exclusive credit of 

 having first constructed the magnetic spool or bobbin, that 

 form of coil since universally employed for every application 

 of electro-magnetism, of induction, or of magneto-electrics. 

 . . . By means of the Henry ' spool ' the magnet, almost at a 

 bound, was developed from a feeble childhood to a vigorous 

 manhood, and so rapidly and generally was the new form in- 

 troduced abroad among experimenters, few of whom had ever 

 seen the papers of Henry, that probably very few indeed have 

 been aware to whom they were, really indebted for this familiar 

 and powerful instrumentality. . . . 



" But, in addition to this large gift to science, Henry has the 

 pre-eminent claim to popular gratitude, of having first worked 

 out the differing functions of two entirely different kinds of 

 electro-magnet : the one surrounded with numerous coils of no 

 great length, designated by him the ' quantity ' magnet ; the 

 other surrounded with a continuous coil of very great length, 

 designated by him the * intensity ' magnet. The former and 

 more powerful system was shown to be most responsive to a 

 single galvanic element (a * quantity battery ') ; the latter 

 and feebler system was shown to be excited by a battery of 

 numerous elements (' an intensity battery ') ; but at the same 

 time was shown to have the singular capability, never before 

 suspected or imagined, of subtile excitation from a distant 

 source. 



"But this was not all. In this distinction between the two 

 magnets Henry discovered the law that there must be a pro- 

 portion between the aggregate internal resistance of the bat- 



* Sturgeon for this received, in 1825, the silver medal of the Society for 

 the Encouragement of Arts. 



