230 MEMORIAL OF JOSEPH HENRY. 



(the true foster-father of the magnet) thus heralds the Yale College 

 triumph : " By dividing about 800 feet of conducting wire into 26 

 strands and forming it into as many separate coils around a bar of 

 soft iron about 60 pounds in weight and properly bent into a horse- 

 shoe form, Professor Henry has been enabled to produce a 

 magnetic force which completely eclipses every other in the whole 

 annals of magnetism; and no parallel is to be found since the 

 miraculous suspension of the celebrated oriental impostor in his iron 

 coffin."* 



The first Electro-magnetic Engine. Among his ingenious applica- 

 tions of the new power, Henry's invention of the Electro-magnetic 

 Engine should here be noticed. In a letter to his friend Professor 

 Silliman, he says : " I have lately succeeded in producing motion 

 in a little machine, by a power which I believe has never before 

 been applied in mechanics, by magnetic attraction and repulsion." 

 The device consisted of a horizontal soft iron bar, about seven 

 inches long, pivoted at its middle to oscillate vertically, and closely 

 wrapped with three strands of insulated copper wire, whose ends 

 were made by suitable extensions to project and bend downward at 

 either end of the beam in reversed pairs, so as conveniently to dip 

 into mercury thimbles in connection with the plates of the battery. 

 Two upright permanent magnets having the same polarity, were 

 secured immediately under the two ends of the oscillating bar, 

 but separated from them by about an inch. So soon as the circuit 

 was completed by the depression of one end of the oscillating electro- 

 magnetic bar, a repulsion at this end co-operating with an attraction 

 at the opposite end, caused immediately a contrary dip of the bar, 

 which by reversing the polarity of this magnetic beam, thus pro- 

 duced a constant reciprocating action and movement. The engine 

 beam oscillated at the rate of 75 vibrations per minute for more 

 than an hour, or as long as the battery current was maintained. f 

 This simple but original device comprised the first automatic pole- 



* Philosoph. Magazine ; and Annals, March, 1832, vol. xi. p. 199. HENRY'S "quantity" 

 magnet was at once adopted by FARADAY in his researches, as well as by the conti- 

 nental electricians; and his device of multiple coils is still recognized as the system 

 best adapted for powerful magnetization. See " Supplement," NOTE D. 



fSilliman's Am. Jour. Sci. July, 1831, vol. xx. pp. 340-343. 



