387 
on the rate of chronometers. 
being again detached, its rate was restored to + 6!' .6, agree- 
ing within o."i of its former detached rate. These mean rates 
were determined in each case for five days. Hence, by con- 
trasting the results obtained under the receiver of the air 
pump with those produced in the condensing engine, it will 
appear, that the chronometer gained in each experiment by 
diminishing the density of the air, and, on the contrary, lost, 
by increasing it. 
In the next experiment the box chronometer M was placed 
in the condensing engine, under pressures corresponding to 
the mercurial columns recorded in the following table ; and 
from which resulted an alteration of rate from ■ — 6". 9 to 
— ; 
Experiments with Box Chrono- 
meter M. 
Mean 
Temp. 
Mean 
Pressure. 
Number 
of days. 
Mean daily 
rate of M. 
O 
49 
30 in. 
5 
// 
— 6.9 
48 
36 in. 
5 
— 8.3 
48 
42 in. 
6 
— 9-5 
47 
48 in. 
5 
— 10.8 
48 
54 in. 
6 
— 16.1 
This chronometer, when placed under the receiver of the 
air pump in air of a less density than the ordinary state of the 
