on the rate of chronometers. 389 
are decrements ; whereas, in the experiments performed in 
the rarified air with the same chronometers, they were uni- 
formly found to be increments ; and hence, the results agree 
precisely with those recorded respecting the time-keepers 
H and M. The almost perfect restoration of the detached 
rates, after the great changes produced by so considerable an 
augmentation of density as that corresponding to the mer- 
curial column of 75 inches,' is a very remarkable feature of 
the table. 
3. To obtain alterations of rate of the most striking and 
remarkable kind, the effects of suddenly removing chrono- 
meters from condensed into rarefied air, and vice versa , were 
estimated by a series of careful experiments. 
A box chronometer, N, having its detached rate exactly 
coinciding with mean time when the barometric column was 
29.95 inches, on being placed in air of a double density 
altered its rate to — 8 ".6 ; and when afterwards placed under 
the receiver in air corresponding in density to an inch of 
mercury, the daily average became -{- 10". 7 ; the difference 
in the densities having produced an alteration of 19". 3 in the 
rate. The observations were continued for each experiment 
five days ; and the changes in the rates were produced imme- 
diately after the time-keeper was removed from one condi- 
tion to the other. In another experiment with the same chro- 
nometer, the mean of six days, under a pressure denoted by 
15 inches of quicksilver, gave a result of -f- 4".i ; but on 
placing it in air, having three times the mean density of the 
atmosphere, the average of the same number of days was 
— 16". 7. Hence it appears, that by removing the time- 
