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504 only from 30 to 40 at most: ''nevertheless, these feeble magnets furnished me with a mechanical action equal to half the force of a man. To maintain this action, during eight hours, scarcely half a pound of zinc is required, everything being properly arranged.''

I have not yet been able to construct a larger apparatus, and I therefore wished to make as much use as I could of the one I possessed, since it was capable of showing completely the nature of the active forces. My experiments may be easily repeated; all depending upon carefully attending to the construction of the commutator, and likewise that of the galvanic apparatus. Those who are acquainted with electro-magnetic phænomena will easily be able to make the necessary arrangements, and to give the accurate proportion to the several parts. The object of this memoir will be attained if it inspire an interest for a subject which merits it.

Königsberg, August 21, 1835.

In November 1834 I had the honour to lay before the Academy of Sciences of Paris a note upon a new electro-magnetic apparatus. That note was read at the meeting of December 1st; and an abstract of it was printed in the Institute, No. 82, of December 3rd, to which I refer. Since that time MM. Botto and dal Negro have claimed the priority of the invention, the former in the Institute (No. 110) of June 17th. The competition in which I find myself engaged with such distinguished men serves only to confirm my conviction of the importance of this new motive power. A discussion as to priority is only of historical interest. It is not astonishing that persons, who had scarcely any communication with each other, should have devoted themselves almost at the same time to the study of the same object. But we ought not to conceal from ourselves that, after the grand discovery of M. Oersted and the experiments of Mr. Sturgeon, who, it seems to me, first gave a great magnetic intensity to soft iron by means of an electric current, and viewing the instantaneous manner in which this magnetism may be destroyed or reversed, by merely changing the direction of the current,—it was not difficult to conceive the possibility that some motion or some mechanical operation might be produced by the electro-magnetic excitation of soft iron. In short we must award the palm to M. Oersted; whilst we who follow him shall have the merit of having known how to apply this new power to practical purposes and the wants of life: and this will be reserved for him who shall best have understood the mechanical and physical principles of this motive power.