608 
ARTICLE XXX. 
On the Laws according to which 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 EK. Lenz. 
From the Mémoires del Académie Impériale des Sciences de St. Petersbourg, 
vol. ii., 1833, p. 427. Read on the 7th of November, 1832*. 
From 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 
Ampeére 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 experimentst+, I first proposed 
to myself to find out in what manner the phenomena 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 thickness 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 phenomenon ; and this determination, toge- 
ther with the necessary consequences following from it, are contained 
in this present memoir. 
* Translated from the German by Mr. W. Francis. 
+ In this repetition { obtained the spark beautifully by means of a spiral 
of a wire 70 feet in length and 0-044 inch thick. The apparatus was formed 
after the one described by Nobili, so that the horse-shoe magnet (of 22 Ibs. 
lifting power) caused of itself the closing of the current. 
