OF ELECTEOSTATIC WITH ELECTEOMAGNETIC FOECE. 
651 
error, as the difference of potentials between the two disks is measured by the current in 
the galvanometer, through a known resistance, independently of any leakage. 
All that is essential to accuracy is that the position of equilibrium before making con- 
tact should be at true zero, the same as when there is no electrical action, and that this 
equilibrium should not be disturbed when simultaneous contact is made with both 
batteries. 
Experiments on May 8. S' = 1710 Ohms. 
Number of 
experiment. 
Great 
battery-cells. 
Small 
battery-cells. 
Distance of disks 
by micrometer. 
Resistance of 
sbunt S. 
Value of v in 
Ohms. 
1 
1000 
6 
12-41 
6870 
28-591 
2 
1000 
6 
12-36 
6940 
28-430 
8* 
1800 
8 
16-99 
5074 
28-886 
9 
1800 
8 
17-02 
5110 
28-686 
10 
1800 
8 
19-91 
4430 
28-910 
11 
1800 
7 
20-07 
4410 
28-850 
12 
2600 
9 
25-08 
3700 
28-762 
13 
2600 
9 
25-12 
3690 
28-795 
14 
2600 
9 
25-29 
3680 
28-735 
15 
2600 
9 
25-18 
3690 
28-752 
16 
2600 
9 
25-19 
3695 
28-709 
17 
1800 
7 
19-69 
4435 
29-474 
Mean value of y=28‘798 Ohms, or B. A. units, 
or 288 000 000 metres per second, 
or 179 000 statute miles per second. 
The “probable error” is about one-sixth per cent. 
Experiments 8, 4, 5, 6, 7 were rejected on account of the micrometer being touched 
during the observation of equilibrium. These experiments gave an average value of v 
=27-39. 
The value of v derived from these experiments is considerably smaller than that 
which was obtained by MM. Weber and Kohlrausch, which was 31-074 Ohms, or 
310 740 000 metres per second. 
Their method involved the determination of the electrostatic capacity of a condenser, 
the electrostatic determination of its potential when charged, and the electromagnetic 
determination of the quantity of electricity discharged through a galvanometer. 
The capacity of the condenser was measured by dividing its charge repeatedly with a 
sphere of known radius. Now, since all condensers made with solid dielectrics exhibit 
the phenomena of “ electric absorption,” this method would give too large a value for 
the capacity, as the condenser would become recharged to a certain extent after each 
discharge, so that the repeated division of the charge would have too small an effect on 
the potential. The capacity being overestimated, the number of electrostatic units in 
the discharge would be overestimated, and the value of v would be too great. 
In pointing out this as a probable source of error in the experiments of MM. Weber 
and Kohlrausch, I mean to indicate that I have such confidence in the ability and fidelity 
* In experiment 8 Mr. Hockin' and I changed places. 
MDCCCLXVIII. 4 U 
