Electromagnetic Induction Machines. 441 



pose of showing the interest which attached to my investiga- 

 tions wherever science is cultivated, and also that when princi- 

 ples are once discovered the similar trains of reasoning of dif- 

 ferent persons lead to similar results, I will here mention that 

 in the month of November 1866 I received a letter from Mr. 

 Moses G. Farmer, of Salem, Mass., U.S.A., on the subject of 

 my researches, and stating that he had built a small machine in 

 which a current from a thermo-electric battery excites the electro- 

 magnet of my machine to start it, and after the machine is in 

 action a branch from the magneto-electric current passes through 

 its own electromagnet, and this supplies the magnetism required. 



The next and last instance of the repetition of this idea to 

 which I shall refer (though my list is not yet exhausted), is that 

 communicated to the Royal Society, February 14, 1867, by Sir 

 Charles Wheatstone, in a paper " On the Augmentation of the 

 Power of a Magnet by the reaction thereon of currents induced 

 by the Magnet itself w *. After pointing out that he had con- 

 structed the electromagnetic part of his machine according to 

 my description, Wheatstone states that he first excites the elec- 

 tromagnet by any rheomotor, and, after removing it from the 

 electromagnet, the circuits of the armature and electromagnet 

 are joined to form a single circuit. The electromagnet, retaining 

 a slight residual magnetism, is therefore in the condition of a 

 weak permanent magnet. The motion of the armature occa- 

 sions feeble currents in the coils thereof, which, after being rec- 

 tified in the same direction by means of a rheotrope, pass into 

 the coils of the electromagnet in such a manner as to increase 

 the magnetism of the iron core ; the magnet having thus received 

 an accession of strength, produces in its turn more energetie 

 currents in the coil of the armature ; and these alternate actions 

 continue until a maximum is obtained. 



I have now enumerated, with some degree of tediousness and, 

 to prevent misunderstanding, as nearly as possible as they 

 have been described, instances where the idea of augmenting 

 the force of a magnet by currents induced by itself has been 

 repeatedly suggested. This enumeration 1 should have deemed 

 somewhat unnecessary were it not that a prominent worker ill 

 science, whose genius and attainments entitle his opinions to a 

 high degree of respect, has described the contrivance (in a man- 

 ner to produce in the minds of those interested in education an 

 erroneous impression) as a new principle in electric science, a 

 great step in magneto-electricity, and the discovery of Messrs. 

 Siemens and Wheatstonef. 



* Proceedings of the Royal Societ}', vol. xv. p. 369. 



t Notes of a course of seven lectures on Electrical Phenomena and 



