and magnetic rotations. 501 
following were the times in which different revolutions were 
performed. 
When the glass disc made 26% 
turns per minute. 
When the glass disc made 191- 
turns per minute. 
Number of 
Revolutions. 
Time. 
Difference. 
Number of 
Revolutions. 
Time. 
Difference. 
O 
.2 S 
•s 
•75 
! « 
21 O 
21 49 
22 15 
22 3O 
// 
49 
26 
*5 
>5 
O 
.25 
.50 
•75 
1 n 
34 0 
34 5 2 
35 20 
35 37 
n 
52 
28 
*7 
*5 
1 
2 
3 
4 
5 
6 
7 
8 
9 
10 
22 45 
23 27 
24 2 
24 37 
25 10 
25 42 
26 12 
26 44 
27 16 
27 45 
42 
35 
35 
33 
32 
32 
29 
38 
30 
1 
2 
3 
4 
5 
6 
7 
8 
9 
10 
35 52 
36 5 ° 
37 35 
38 18 
38 58 
39 37 
40 15 
40 55 
4 1 35 
42 18 
45 
43 
40 
39 
38 
40 
40 
43 
41 
In the latter of these experiments, at the seventh revolu- 
tion, the passing of a carriage may have slightly affected the 
remaining revolutions. 
Experiment 7. 
A thin disc of copper, such as is used for engraving upon, 
about seven inches in diameter, was connected by wax 
with the glass plate employed in experiment 1, and the 
same apparatus was used with a needle of sealing-wax 
suspended above : on making the copper plate revolve 
rather quickly, the needle followed it, and went through two 
revolutions. Several plates of lead, pewter, brass and copper 
were tried, and the results were similar. 
3 T 
MDCCCXXVI. 
