the Pendulum vibrating Seconds in the Latitude of London. 181 
- Distance between the lines on the bar, 49°5 inches. 
| iene a ee ee ee ee 
Highest | Lowest | Diff. of |Division of the|/xpansion in parts of the 
Temp. | Temp. | Temp. | Micrometer. | length for each degree. 
96 | 43 | 53 620 -000010116 
i 93 43 50 580 -0000 10030 
| 
Distance between the lines on the bar, 50°5 inches. 
91 | 43 1 48 | 600 -000010616 
89 84 5 70 -00001 1890 
Al 5 8 89 ‘000009448 
Wf, 6} 14 149 -000009038 
80 44 36 400 -000009 436 
£0 60 20 215 *000009129 
hy fla 60 USe'\ 152 -000009930 
Mean of the whole, | -000009959. 
ee —————— ee een . 
The mean ‘000009959 may be taken as the expansion of the 
pendulum in parts of its length due to a change of temperature 
of one degree of the thermometer. : 
- Of the Method of deducing the Length of the Pendulum 
z vibrating Seconds. 
The distance between the knife edges was taken when the 
standard: seale and the pendulum were both of the same tempe- 
rature ; and as this temperature did not differ considerably from 
6§2°, the difference in the rate of the expansion (if any) between 
the pendulum and the scale may be neglected as perfectly in- 
sensible, and 62° be considered as the temperature of measure- 
ment. 
The number of vibrations made by the pendulum in 24 hours, 
having been determined at a different temperature, the length’ 
of the pendulum will be greater or less as the temperature of 
o»servation exceeds or falls short of 62°; and by applying the 
expansion due to such difference of temperature, derived from 
the experiments contained in the preceding article, the distance 
of the knife edges, or length of the pendulum, will be known for 
the temperature at which the number of vibrations was deter- 
mined, whence the length of the pendulum vibrating seconds 
may be readily deduced, the lengths of pendulums being to each 
other inversely in the duplicate ratio of the number of their vi- 
brations in 24 hours. 
M3 of 
