CAPTAIN RATER’S CONVERTIBLE PENDULUM. 
335 
Whence there appears, as the result of the experiment with the great weight 
below, a difference of 14.88 vibrations per diem, corresponding to a difference 
of atmospheric pressure of 28.406 inches of mercury at 32° ; the temperature 
of the air of full pressure being 49.07, and that of the rarefied medium 48.45. 
And with the great weight uppermost : 
April 23. Previous to the vibration in the 
rarefied medium . 
April 23. Subsequent to the vibration in 
the rarefied medium 
Vibrations. 
860/2.15 
86072.84 
Barom. 29.575 
Barom. 29.602 
Mean 
86072.49 Barom. 29.588 
The vibrations in a rarefied medium reduced 
to the same temperature as those in air 
of ordinary density 
86087-27 
Gauge 2.10 
Difference 
14.78 27.488 
Whence, with the great weight uppermost, there is found a difference of 14.78 
vibrations per diem, corresponding to a difference of atmospheric pressure of 
27-488 inches of mercury at 32° ; the temperature of the air of full pressure 
being 49.35, and that of the rarefied medium 49.9. 
From these results we obtain 15.7 vibrations per diem as the reduction 
to a vacuum for the convertible pendulum, as it was used by Captain Kater, 
vibrating with the great weight below, in air of 49°, under a pressure of 30 
inches of mercury at 32°; and 16.1 vibrations per diem, when inverted, or 
with the great weight uppermost, in air of like temperature and density. 
According to the formula by which Captain Kater reduced the vibrations 
of this pendulum in air to the supposed vibrations in a vacuum, the reduction 
for each position of the pendulum would be the same, and the amount for air 
of the named temperature and density would have a little exceeded 7 vibra- 
tions per diem. 
In the account of Captain Kater’s experiments (Phil. Trans. 1818, page 75) 
it is remarked that on a sudden and considerable change having taken place 
in the hygrometric state of the atmosphere, vibrations which had been previously 
identical in each position of the pendulum ceased to be so ; an effect which he 
attributed to an alteration in the weight of the wooden extremities of the pen- 
