OF ELECTEOSTATIC UNITS IN THE ELECTROMAGNETIC UNIT. 
421 
Temp. 14°*8 C. March 23, 1870. Battery 180 cells. 
Electrometer. 
Difference. 
Mean. 
60-0 
59*4 
59*70 
58-7 
58-7 
58-70 
60*0 
59*55 
59-1 
59*0 
58*9 
58*95 
59*0 
59*0 
59*00 
59*0 
590 
59*00 
Resistance in B. A. 
v in centims. per 
second. 
Electrodynamometer. 
units. 1 = 10 1 ' centims. 
per second. 
Deflection. 
Mean. 
R. 372*5 
L. 370*5 
371*5 
15617 
292*6 xlO 8 
R. 367*5 
L. 367*0 
R. 367*5 
L. 365*5 
367*25 
366*5 
15633 
295*9 x 10 s 
291*7 x 10 8 
R. 364*0 
L. 364*0 
364*0 
15658 
293*6 x 1 0 s 
R. 363*75 
L. 362*75 
R. 361*0 
L. 361*5 
363*25 
361*25 
15673 
293*5 XlO 8 / 
293*0 x 10 8 
The figures in the electrometer and electrodynamometer columns of the above 'Tables 
represent the readings in the arbitrary divisions of the two instruments. To deduce the 
value of v, these readings were reduced to absolute measure by means of the expressions 
for V— V' and y already given. The resistance introduced into the circuit being equal 
to that of the coils, half the difference of potentials indicated by the electrometer was 
employed in the calculations. - 
III. The instruments having been removed to the new laboratory, were again set up 
in the spring of 1871, but no observations were made till September following. 
When the electrometer was set up, a series of weighings was gone through to deter- 
mine the displacement of the movable disk produced by a given force. A long series 
of weighings of May 15th and 16th gave 200T9 micrometer-divisions as the displacement 
due to ’6 gramme. Before the electrometer was again used in September a longer series 
of weighings was gone through : this gave as the mean value of the displacement 200*55 
divisions, and this value was adopted in succeeding measurements. 
The electrodynamometer was set up in the same manner as formerly ; the only altera- 
tion was in the manner of adjusting the lamp and lens, which were now supported and 
adjusted in the manner already described. A new determination was made of the moment 
of inertia of the suspended coil : this had become necessary from an alteration in the 
weight of the coil arising from the loss of a part of the mirror. 
The moment of inertia of the vibrator with which the coil was compared was 4293*772 
centimetre-grammes. The periods of vibration of the vibrator and coil were 25*939 and 
15*5575 seconds respectively. This gave as the moment of inertia of the suspended coil 
1544*6036 centimetre-grammes. After this comparison the mirror of the coil was 
resilvered, and was found to have increased in weight *101 gramme. With this increase 
of weight the moment of inertia of the coil became 1544*704 centimetre-grammes. The 
distance of the scale was made 354*6 centims. The period of vibration of the coil was 
5*823 seconds. With these alterations the value of y became *000020114. 
