PHILOSOPHICAL SOCIETY OF WASHINGTON, 249 



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 mag- 

 netic 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 im- 

 mediately a contrary dip of the bar, which by reversing the 

 polarity of this magnetic beam, thus produced a constant recip- 

 rocating action and movement. The engine beam oscillated at 

 the rate of 15 vibrations per minute for more than an hour, or 

 as long as the batteiy current was maintained.* This simple 

 but original device comprised the first automatic pole-changer or 

 commutator ever applied to the galvanic battery, — an essential 

 element not merely in every variety of the electro-magnetic 

 machine, but in every variety of the magneto-electric apparatus, 

 and in every variety of the highly useful induction apparatus. 



In an interesting " Historical Sketch of the rise and progress 

 of Electro-magnetic Engines for propelling machinery," by the 

 distinguished philosopher James P. Joule, he remarks: "Mr. 

 Sturgeon's discovery of magnetizing bars of soft iron to a con- 

 siderable power, and rapidly changing their polarity by miniature 

 voltaic batteries, and the subsequent improved plan by Professor 

 Henry of 7-aising the magnetic action of soft iron, — developed 

 new and inexhaustible sources of force which appeared easily and 

 extensively available as a mechanical agent ; and it is to the in- 

 genious American philosopher above named, that we are in- 

 debted for the first form of a working model of an engine upon 

 the principle of reciprocating polarity of soft iron by electro- 

 dynamic agency "f 



In Henry's deliberate contemplation of his own achievement, 

 his remarkable sagacity and sobriety of judgment were con- 

 spicuously displayed. Unperturbed by the enthusiasm so natu- 



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



t Sturgeon's Atinals of Electricity etc., March, 1839, vol. iii. p. 430. 

 Sturgeon himself the first to devise a rotary electro-magnetic engine, 

 deserves honorable mention for correcting the statement of an American 

 writer, and declining his mistaken award by frankly recognizing Henry's 

 right to priority. (Atmals of Electricity, April, 1^39, vol. iii. p. 554 ) 



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