397 
on the rates of chronometers . 
may be attributed to the minute aberrations of the chrono- 
meter, produced by imperfections of workmanship, and to 
the errors arising from observation. 
Changes produced in the rate of the time-keeper H,by 
small but irregular decrements in the pressure. 
Mean 
Temp. 
Mean 
Pressure. 
Number 
of Days. 
Mean daily 
rate. 
Difference of 
Pressure. 
Change of 
rate. 
O 
5 1 
49 
inches. 
29.26 
28.30 
4 
4 
+ 8.7 
+ 9-7 
Inches. 
— 0.96 
+ 1 -38 
— 1.68 
+ I.69 
— 1.69 
* 4 “ 2 - 2 5 
— 1.25 
1 .02 
— 0.77 
“I - 0.60 
— 0 .66 
if 
+ 1.0 
O 4 . 
47 
4 6 
29. 8 
28.00 
4 
4 
+ 9-3 
+ 10-7 
+ 1.4 
1 
45 
48 
29.69 
28.00 
4 
4 
-f 9-4 
-f 10.6 
+ 1.2 
-{- 1.2 
+ 0.4 
— 0.3 
-§- 0.5 
— 0.4 
+ 0.6 
47 
44 
30.25 
29.00 
4 
4 
H“ 9-4 
+ 9-8 
43 
42 
30.00 
29.25 
4 
4 
+ 9-5 
-f- 10.0 
O O 
29.85 
29.25 
4 
4 
+ 9.6 
+ 10.2 
From these experiments it may be therefore inferred, that 
a difference in the density of the atmosphere, represented by 
a quantity less than an inch of quicksilver, if continued for 
a day, was capable of affecting all the chronometers em- 
ployed; and this is an atmospheric change by no means 
uncommon in this variable climate. Nor is it indeed neces- 
