618 LENZ ON ELECTRO-MAGNETISM. 
By means of formula (A.) we shall therefore obtain for the narrow spi- 
rals 
w= (L +/+ dA)p-sin. d.a@ = 701-25-p: sin. (13° 7), 
for the wide spirals 
a’! =(L +1 +4A!)p-sin. 1 a! = 876-25 - p-sin. (11° 21’), 
therefore the relation of the electromotive powers, or 
eet Oe ee 
x 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 
| Angle of deviation. Mean 
or @ 
1 2B iA 
Narrower! | sree 
dais 13-1 |15°8 
Wider 
convolutions. 
12°8 |12°4.| 13°52 | 19°2 | 692°45 
| 
\ 7:1| 8°7| 7-1| 8°7| 7-90 |549°2 | 1229-75 
| 
we! | 129975 * sin. (3° 52’) 
“@ 699-45 - 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 thing proved by experiment, the position, that 
“the electromotive power which the magnetism 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- 
therefore =e Ol One 
