618 



LENZ ON electro-ma(;netism. 



By means of formula (A.) we shall therefore obtain for the narrow spi 

 rals 



x=z(L + I + X)p • sin. i a = 701-25 -p • sin. (13° 7')> 

 for the wide spirals 



x' = (L + / + X')jo - sin. ia'= 876-25-;; -sin. (11° 21'), 

 therefore the relation of the electromotive powers, or 

 x^_ 876-25 • sin. (11° 21') 



X 



'= 1-0838, 



701-25 - sin. (13° 7') 

 therefore not deviating much from 1, that is, the electromotive power 

 is in both spirals the same. 



I endeavoured in a more striking manner to confirm this position by 

 the following experiment : I wound the wire No. 2 in six convolutions 

 round a great wooden wheel of 28 inches in diameter, and placed the 

 wheel on the iron cylinder. After having completed, as in the former 

 cases, the experiment, I wound also six convolutions of the same wire 

 immediately round the same iron cylinder, where also, as above, the 

 convolutions again were 0-73 inch in diameter. The experiment gave 



therefore 



x' _ 1222-75 - sin. (3° 52') 



= 1-0107 



692-45 • sin. (6° 45'-5) 

 Here the proportion of both electromotive powers approaches still 

 more nearly to unity than in the former case, although the proportion 

 of the diameter of the spirals is = 1 : 38-3. We may therefore regard 

 as a tiling proved by experiment, the position, that 



"///e ckctromotive power which the maynetism produces in the sur- 

 rounding spirals is the same for every magnitude of the convolutions." 

 Since however a spiral wire inclosing the armature presents to the 

 action of the magnetism in the armature a length greater in proportion as 

 its diameter or its distance from the armature is greater, it follows from 

 the law just discovered that the electromotive action of the magnet upon 

 one and the same particle of the wire decreases in the simple ratio of 

 the distance. This is as it were the reversal of the law demonstrated 

 by Biot in the field of electro-magnetism, which, as is known, states 

 that the action of an electric closing wire upon a magnetic needle de- 

 creases in the simple ratio of the distance ; and it follows from our ex- 



