603 



Article XXX. 



On the Laws accordmg to ivliich the Magnet acts upon a Spiral 

 when it is suddenly approached to or removed from it ; and 

 on the most advantageous mode of constructing Spirals for 

 Magneto-electrical purposes ; by E. Lenz. 



From the Memoires de I'Jcademie Imperiale des Sciences de St. Petersbourg, 

 vol. ii., 1833, p. 427. Read on the 7th of November, 1832*. 



X* ROM the great interest which the late discoveries of Faraday in 

 the field of electro-magnetism must awaken in all the natural philoso- 

 phers of Europe, it is to be expected that we shall soon receive many 

 and various explanations of the momentary action of an electric cur- 

 rent on an electrical conductor; and as it is allowed according to 

 Ampere to reduce the action of a magnet entirely to that of circular 

 electric currents, the same may be expected with respect to the action 

 of the magnet upon such a conductor. Up to the present moment we 

 here in the north are only acquainted with the papers of Becquerel, 

 Ampere, Nobili, and Antinori and Pohl ; and as none of these authors 

 have occupied themselves with that branch of the subject to which I 

 have directed my particular attention, I hasten to make known as 

 quickly as possible the following contribution to the science of mag- 

 neto-electrism. 



After having repeated Faraday's chief experimentsf, I first proposed 

 to myself to find out in what manner the phaenomena of the magnetic 

 action on a spiral suddenly approached or removed might be produced 

 in the easiest and most powerful manner. For this purpose I had to 

 determine what influence 



1. The number of coils, 



2. The breadth of the coils, 



3. The tliickness of the wire, 



4. The substance of the coils, 



of the electromotive spirals (i. e. of those which are acted upon by 

 the magnet) had upon the phaenomenon ; and this determination, toge- 

 ther with the necessary consequences following from it, are contained 

 in this present memoir. 



* Translated from tlie German by Mr. W. Francis. 



f In this repetition I obtained the spark beautifully by means of a spiral 

 of a wire 70 feet in length and 0-014 inch thick. The apparatus was formed 

 after the one described by Nobili, so that the horse-shoe magnet (of 22 lbs. 

 lifting power) caused of itself the closing of the current. 



