HISTORY OF ELECTRICITY IN AMERICA 115 



of exhaustive research ; the maximum efficiency of a galvanic 

 couple, and the cost of a system of motive power depending 

 upon the consumption of zinc, also received from his hands 

 that sufficient treatment which leaves nothing to be desired. 

 The last named investigations were instigated by his success, 

 in 1831, in constructing an electromagnetic motor — the first of 

 its kind that the world had ever seen. Though of great 

 historic importance, the apparatus, which is still to be seen 

 at Princeton college, possesses now merely an antiquarian 

 interest. 



In the same year Henry set up in '' one of the upper rooms 

 in the Albany academy," the first electromagnetic telegraph. 

 The circuit was more than a mile long, and the sounder was a 

 bell. For striking the bell he employed a pivoted steel bar, 

 permanently magnetized, and ''placed with its north end be- 

 tween the two arms of a horseshoe magnet." ''When the 

 magnet was excited by the current," continues Henry, in his 

 own account of the experiment, "the end of the bar thus 

 placed was attracted by one arm of the horseshoe, and re- 

 pelled by the other, and was thus caused to move in a hori- 

 zontal plane, and its farther extremity to strike a bell suitably 

 adjusted." 



In view of this experiment at Albany, it is often asserted 

 that the credit of originating the electromagnetic telegraph, 

 by which is meant the telegraph in all essential features as we 

 know it to-day, is due to Joseph Henry. But in making such 

 a claim, the fact is overlooked that this apparatus of Henry's 

 resembled the needle telegraph which Ampere invented a 

 dozen years before, nearly as much as it did the telegraph of 

 Morse and Vail. Henry's steel bar was in effect nothing more 

 or less than Ampere's magnetic needle. It is not difficult to 

 see that the introduction of the electromagnet as an inter- 

 mediary between the coil and the needle gave the apparatus 

 greater power and begot other mechanical advantages, 

 adapting it, for example, to be used more readily for a striker ; 

 but Henry's invention remained, in part, a needle telegraph, 

 having in some measure the comparative insufficiencies which 

 have resulted in the gradual displacement of the needle by the 

 electromagnet for signalling purposes. There was still lack- 



