38 3 
on the rates of chronometers . 
The mean also of five days observations with chronometer 
H, in a medium corresponding in density to 25.95 inches of 
mercury, being the average state of the barometer at the 
Palace of Ildefonso, 630 fathoms above the ocean, produced 
an increment in its rate amounting to 3 /# .o ; and which taken 
in conjunction with the results of the same chronometer re- 
corded in the preceding table, prove that it’s rate varied 
nearly with the density of the medium in which it was placed. 
This chronometer is one, on which in many delicate inquiries 
I particularly depended. 
Although it. appears from the preceding experiments, that 
the alterations of rate in the same chronometer depend on 
the density of the medium in which it is placed ; yet the 
magnitudes of the changes in different time-keepers appear 
o be very unequal, arising no doubt from peculiarities of 
construction. Thus, a set of experiments was undertaken 
with two good box chronometers, in order to discover what 
changes would, take place in their rates if they were trans- 
ported from Vera Cruz, on the shores of the Pacific Ocean, 
to the Table Land of Mexico, where the mean atmospheric 
pressure is denoted by 23 inches of the barometer. The 
result proved, that the change in the rate of the chrono- 
meter represented by K, amounted only to + 1 "9, and in 
the time-keeper L, to — 5 ".q ; the former having gained by 
the diminished pressure, and the latter lost. 
