36 
mean of the first and third. Five determinations of the 
resting point were usually made with the excess to he 
measured alternately added and removed. From these five, 
three values of the deflection (n) due to the excess were 
calculated in a manner which will be seen from the example 
below. 
The time of vibration .. — This was found from several 
determinations of the time of ten oscillations. The method 
will be seen from the example. No correction was needed 
for the resistance of the air as long as the vibrations did 
not exceed two divisions of the scale. When however they 
were much more than that the time of vibration was found 
to increase with the arc. As the time of vibration fre- 
quently changes slightly, probably through variations of 
temperature, it was usually observed before and after the 
determination of the deflection (n) and the mean of the two 
taken as the true time. 
The following example of the determination of the value 
of a centigramme rider by placing it half way along the 
beam wifi sufficiently explain the details of the method. 
TIME OF VIBRATION AT COMMENCEMENT, 
POINTER APPARENTLY MOVING FROM POINTER APPARENTLY MOVING FROM 
LEFT TO RIGHT. RIGHT TO LEFT. 
No. of 
Vibration. 
Observed time 
of passage of 
pointer through 
resting point. 
No. of 
Vibration. 
Observed 
time of 
passage of 
pointer 
through 
resting p’t. 
Time of 10 
Vibrations. 
No. of 
Vibration. 
Observed time 
of passage of 
pointer through 
resting point. 
No. of 
Vibration. 
Observed 
time of 
passage of 
pointer 
through 
resting p’t. 
Time of 10 
Vibrations. 
0 
llh 15' 36" 
10 
17' 43" 
127 
1 
llh 15' 49" 
11 
17' 56" 
127 
2 
16' 1" 
12 
18' 8" 
127 
3 
16' 14" 
13 
18' 21" 
127 
4 
16' 25"-5 
14 
18' 33" k 5 
127, 
5 
16'39"-5 
15 
18' 46" 
126-5 
6 
16' 52" 
16 
18' 59" 
127 j 
7 
17' 5" 
17 1 
19' ll"-5 
126-5 
Mean value of 10 vibrations.. 
1271 
1 
Mean value of 10 vibrations.. 
12675 
Mean of means 126-875. 
i, = 12-6875" 
