499 
copper and other substances during rotation, 
show that the magnetism in the disk is instantaneously deve- 
loped by one pole of the magnet, and as instantaneously de- 
stroyed, and a contrary magnetism developed by the contrary 
pole ; or rather it would indicate, that the time during which 
the disk retained the induced magnetism was less than the 
time of half a revolution of the magnet. 
The same two bar magnets were laid horizontally by the 
side of each other, inch a part. They were first made to 
revolve rapidly under the disk with their poles of the same 
name adjacent, and then with those of a contrary name 
adjacent. 
No. of 
revolutions. 
Poles of the same name 
adjacent. 
Poles of a contrary name 
adjacent. 
Screw. 
Unscrew. 
Screw. 
Unscrew. 
Time. 
Time. 
Time. 
Time. 
m. s. 
m. s. 
m. s. 
m. s. 
1 
29 
28 
31 
32 
2 
40 
57 
42 
46 
3 
48 
46 
52 
58 
4 
56 
53 
I 01 
I 07 
5 
I 03 
I 00 
I 1 1 
» 15 
6 
1 10 
I 06 
1 18 
I 23 
7 
I 16 
I 12 
I 25 
1 30 
8 
1 21 
I 17 
* 31 
1 36 
9 
I 26 
1 22 
* 37 
I 43 
10 
I 31 
I 27 
I 43 
I 49 
From these it appears that the effect was but little dimi- 
nished by placing poles of a contrary name so close to each 
other. 
The adjacent poles being of the same name, they were 
connected by a piece of soft iron i inch thick, and i inch 
wide. After 4|- revolutions of the disk (screw), the torsion 
of the wire was equal to the force of the magnets, and the 
MDCCCXXV. 3 T 
