CAPTAIN KATER'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 thel q-^^So",'-, n ^r^ ^^r 



rarefied medium |860/2.1o Barom. 29.575 



April 23. Subsequent to the vibration in ") q^^-o oa -n «« i-r^^ 



the rarefied medium / ^^^^2.84 Barom. 29.602 



Mean 86072.49 Barom. 29.588 



The vibrations in a rarefied medium reduced "| 



to the same temperature as those in air > 86087-27 Gauge 2.10 

 of ordinary density J 



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 mercuiy 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 Rater'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- 



