108 REPORT—1890. 
The galvanometer was one constructed in the laboratory; it had a 
resistance of 17,600 ohms, with a long silk fibre suspension—a quartz 
. fibre would have been an improvement. 
Its sensitiveness was such that 1 scale division corresponded to 
83 x10-!° C.G.S. units of current; the time of swing was 7:2 seconds, 
so that the sudden discharge through the galvanometer of 10—!° C.G.S. 
units of electricity produced a throw of 1 division; or, in other words, the 
quantity which, when discharged suddenly through, gave a throw of y 
divisions was yx10-!°. This was determined by discharging through 
the galvanometer a condenser of capacity ‘1 microfarad ; when charged to 
1 volt, the throw observed was 100 divisions, while the steady current 
due to an E.M.F. of ‘001 volt produced a deflection of 72 divisions. 
_The observations were made by varying c. There was a commutator 
in the battery circuit. In each position of this commutator two values 
of ¢ were taken and the corresponding resting points of the spot on the 
scale observed. From these the value of c, which corresponded to the 
zero position of the spot, was obtained by interpolation. 
These observations were made twice for each position of the commu- 
tator, and the mean taken. 
We will give one series as an example :— 
August 27, 1890.—Temperature of standard fork, 18°°8. 
55 Beats my » 20 in 65:4 seconds. 
” ” ” ” ” 20 in 65:2 ” 
Condenser No. 1. 
Frequency, 80 approximately. 
pee owol ae Zero Reading Resistance Resting Point 
iG 48 5880 51 
be as 5800 i) 
/ Bie age : 
x 49 15890 50 
Temperature of coils, 17°°5. Beats, 20 in 64°8 secs. at 19°3. 
It will be seen that between the third and fourth series the galvano- 
meter zero has shifted slightly. 
From these we get as the four values of c the following :— 
5887°5 
5886°6 
5888°3 
5887°5 
Mean, 5887°5 at 17:5 
Correction to 17°, 9 
Value of c= 5888-4 at 17°, 
while the beats are 20 in 65 seconds at 19°, or ‘307 per 1 second; at 19° 
the frequency of the standard is 128-066 ; thus the frequency of the driven 
fork is 128:066—-307, i.e., 127°759. Thus for the driving fork we have 
the octave below this, or 63°879, while the frequency of the commutator 
is 5/4 of this. 
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