ELECTRO-MAGNETISM AS A MECHANICAL POWER. 535 



filled with mistrust on obsei-ving tliat this thought, which appeared to 

 me so simple and natural, was not mentioned by any of the numerous 

 natural philosophers who occupy themselves so assiduously with electro- 

 magnetic experiments. I could not believe but that these notions must 

 have struck them ; but I was forced to suppose that they had either seen 

 immediately the impracticability of them, or that, even if they had made 

 some experiments upon the subject, they had met with insurmountable 

 difficulties in its application. This long deterred me from making any 

 experiments ; but in the lecture which I gave before this Society on the 

 10th of December 1832, I could not refrain, when speaking of the 

 powerful electro-magnets of Henry and Ten Eyck, from asking the 

 question, "whether such a considerable power as that which is ob- 

 tained by interrupting the electric current and then restoring it, could 

 not be applied with advantage to mechanical science." After that lec- 

 ture I considered the subject again, and thought I had convinced myself 

 of its practicabilit}^ ; but that even if it were so, the result could not be 

 very important, because the motion of the keeper must necessarily be 

 very small. Notwithstanding, I had a more powerful electro-magnet 

 made than any I had hitherto jjossessed, with which I intended to try 

 the experiment ; and I regarded the expense the less, as this apparatus 

 appeared to me at the same time to be very appropriate for the evolu- 

 tion of the currents observed by Faraday ; for this purpose the arma- 

 ture also must be covered with copjjer wire, and then each time the 

 poles of the electro-magnet are reversed, a magneto-electric current 

 circulates through this wire. In the mean time I found another method 

 whereby the object I had in view might be effected, and which would 

 allow a greater degree of motion to the armature : I thought I could 

 effect this in the following manner. I placed on the table two cylin- 

 drical soft- iron horseshoes bound round with similar wires; so that when 

 the electrical current was transmitted through both wires, the similar 

 poles should lie oppo^te to each other: between these, and at a 

 small distance from either, I placed a cylinder of soft iron, serving for a 

 keeper; and then I expected to see the armature play to and fro between 

 the two electro-magnets when I sent the electric current first round the 

 one and tiien round the other electro-magnet. After several fruitless 

 rough experiments it succeeded at last, and I therefore then instructed 

 a turner to make an apparatus, that I might be able to repeat, by means 

 of it, in a more easy and perfect manner, these yet very imperfect ex- 

 periments. I had proceeded so far, when, on the 4th of January, I 

 received the latest part of Baumgiirtner's Zeitschrift, published at 

 Vienna on the 17th of November 1832. I there observed a treatise, 

 iiititled, " Electro-magnetic Experiments of Salvatore Dal Negro, Pro- 

 fessor of Natural Philosophy in the Imperial University at Padua," 

 (translated from the Italian). The author says in the Introduction : 

 " Philosophers have already known for some time the jxjwer of elec- 



