407 
on the rates of chronometers. 
detached state. By augmenting the quantity of air to an 
atmosphere and a half, the daily variation still presented the 
same quantity ; but on removing the chronometer into the 
receiver under a pressure of 13 inches, the rate became 
— if' .3 ; and with a pressure of 12 inches, — 8 ". 8 . Hence 
it appears, though the experiment is too limited to draw from 
it any general conclusion, that in this particular case, no alte- 
ration of rate took place by increasing the density of the 
air above its average state ; but by diminishing it below the 
same point, the rate was accelerated. 
It may be proper however to advert to a circumstance, 
which may be regarded as having possibly exercised some 
influence on the foregoing results ; and that is, the change of 
temperature always attendant on sudden alteration in the 
density of the air. 
When the chronometers were placed, for example, beneath 
the receiver of the air pump, a sudden diminution of tempe- 
rature was in all cases- produced, proportional to the degree 
of exhaustion ; and on restoring the medium to its original 
density, an elevation of temperature resulted, equally rapid 
in its effects. So also when the time-keepers were placed in 
the condensing engine, the sudden compression of the atmo- 
sphere, produced an immediate liberation of caloric, and which 
was followed, when the equilibrium of air was renewed, by 
a depression of temperature below its original condition. 
These alterations of temperature, although producing a 
change of only two or three degrees, in a delicate thermo- 
meter, are nevertheless regarded by Mr. Dalton as the ef- 
fect of a much greater degree of heat ; but which is permit- 
ted to impart its influence only for a very few seconds, in 
