390 Mr. Harvey on the effects of density of air 
keeper from condensed into rarefied air, it gained ; and con- 
versely, from rarefied into condensed air, it lost. 
In a third experiment, the pocket chronometer O, gave a 
mean rate of — 6 ". 5 when placed in air of a density denoted 
by 2 6 inches of the mercurial column ; but when placed in 
the condensing engine, in air of a density denoted by 45 
inches of quicksilver, the rate changed to — 2". 7; and on 
afterwards restoring it to the ordinary pressure of the atmo- 
sphere during four days, the average rate became — 7". 7. 
The character of this chronometer, during many preceding 
experiments, was to gain with greater pressure, and to lose 
with less; and the preceding experiment perfectly accords with 
the same results. 
In a fourth experiment, the pocket chronometer C was 
employed, having a mean rate of -f- i".2 when placed for six 
days under the receiver in air corresponding in density to 
28 inches of mercury ; but on introducing the time-keeper 
into the condensing engine, in air of a density denoted by 60 
inches of quicksilver, the rate immediately declined to 
— 8". 2. In a converse experiment with the same chronometer, 
the rate was first determined in the condenser when the 
density corresponded to 36 inches of mercury, the average 
being + o".7 ; but on removing it into the receiver, and ex- 
hausting the air until the mercurial gauge sunk to 27 inches ; 
the mean of four days observations gave an augmented rate 
of - J - s '' -9 ; and on restoring the chronometer to air of the 
ordinary density, its mean rate became -}- 2". 6, agreeing 
within half a second of its original detached rate. This time- 
keeper, in many antecedent experiments, had always been 
