406 Mr. Harvey on the effects of density of air 
of the mercurial column, when the daily rates were — i6".o, 
— 15". 7, and — 16". o. In another 4 instance, a time-keeper 
maintained a steady rate of — 10". 5 under a pressure of 
40 inches. During one day some of the air escaped, and the 
rate became — 7 f, .o. The machine was then repaired and 
the former pressure restored, when the rate returned to 
— 10". 3. On the third day air again escaped, and the rate 
changed to— - 8 ", 5; but on the fourth day the condenser 
being in perfect order, the time-keeper again returned to 
— 10". 7. Thus, even from the temporary imperfections of 
the air pump and condensing machine, may proofs be drawn, 
demonstrating the effects of atmospheric pressure on the 
rates of chronometers. 
An experiment was also attempted, at the suggestion of 
Mr. Davies Gilbert, to discover if, by removal of the case 
of a chronometer, and presenting its balance and spring to the 
free action of the air, the effect on the rate would present a 
result analogous to that which it would furnish under ordi- 
nary circumstances. With the case of the time-keeper in its 
proper situation, and the full pressure of the atmosphere on 
the machine, the rate of six days was — 15".3; but under 
the receiver with the mercurial gauge at 26 inches, it became 
for a like period — 13" '.6. By removing the case, the de- 
tached rate became — 1 6"4 ; and under the receiver, with 
the pressure of 2 6 inches, the rate was — i5' # .8 ; the removal 
of the case having in both instances increased the losing 
rate of the machine. On placing the time-keeper in the con- 
densing machine under a pressure of an atmosphere and a 
quarter, the case being still removed, the rate was found to 
be — 15". 5, differing but little from that determined in its 
