IN THE OBSERVATORY OF GREENWICH. 
475 
at 30°, pp. 46“ and 469, to compare with the rate at 57° which has been de- 
duced as above from the experiments in the preceding- August and September. 
The position of the slider in the winter experiments was at 1.6 ; consequently 
the result is strictly comparable with the mean of the two results H to M, and 
W to EE, made in summer, in one of which series the slider was at 1.633, and 
in the other at 1.566, the mean of which is 1.6. But in fact a small change 
of position of the slider when the weight is below, has so little influence on 
the rate, that had there been even a slight difference it might have been safely 
disregarded for the purpose now in view. 
• . • ° 
Winter experiments . . . 86081.00 vibrations at 30 
Summer experiments . . . 86069.07 * 57 
Differences. . . 11.93 27 
Equivalent to 0.441 for each degree of Fahrenheit. 
In the Phil. Trans, for 1830, Art. XIX. I have reported the results of a similar 
comparison of the rates of an invariable pendulum, made also of plate brass, in 
winter and in summer ; by which it was shown that a degree of Fahrenheit 
corresponded to a change of 0.44 in the rate of that pendulum also. These 
two results are strongly confirmatory of each other. 
It results, then, that the vibrations of Captain Rater’s pendulum, which at 
5 7° have been found 86069.10, are 86066.90 at 62°. The distance between the 
knife edges as measured by Captain Rater is 39.44085 inches of Sir George 
Shuckburgh’s scale, the pendulum and scale being at 62°. The vibrations in a 
vacuum corresponding to this distance are 86066.90, the temperature of the 
pendulum being 62°. We have then for the seconds pendulum in the Royal 
Observatory, at 62° and in a vacuum. 
In 86066.90 : 39.44085 : : 86400 : 39.13734. 
