39 s Mr. Harvey on tine effects of the density of air 
9 " .5, and the latter a rate of a similar kind of io".4. Know— 
ing the merits of these chronometers, I ventured to predict, 
that if they were removed from the condensed air into an 
atmosphere corresponding in density to 21 inches of quick- 
silver, the transition would produce rates greater than those 
corresponding to 23 inches, in consequence of the time-keeper 
being placed by such an experiment in air of a less density 
than that corresponding to the first experiment. The result 
verified the conjecture ; the average rate of the time-keeper C 
having become -J- 5 #/ .o, and that of Chronometer D -f- ia".o. 
These interesting results are recorded in the next table. 
Experiments with the chronometers C and D, 
when removed from rarefied into condensed 
air, and vice versa. 
Mean 
Temp. 
Mean 
Pressure. 
Number 
of Days. 
Mean daily 
rate of C. 
Mean daily 
rate of D. 
47° 
23 in. 
5 
+ * # 5 . 
+ 9 /; - 4 
O 
49 
60 in. 
5 
- 7 ".o 
— 1*0 
0 
00 
21 in. 
5 
+ 5 ".o 
+ 1 2 ,/ „0 
1 
By contrasting also the rates of the chronometers B and C, 
when subjected, as in two of the preceding experiments, to 
air corresponding in density respectively to half an inch, and 
7 5 inches of quicksilver ; it will be perceived, that the effect 
of these opposite densities was to occasion an alteration of 
40". 7 in the rate of the time-keeper B, and of 28". 1 in that 
of C. These results are recorded in the next table. 
