374 Mr. Harvey on the effects of the density of air 
highly rarefied air in which the last experiment placed it, 
to the full pressure (29.85 inches) of the atmosphere, the 
mean of ten days observations gave an average rate of 
— 6 ". 3 ; the time-keeper having altered its detached rate 
- — 3 ". 2, in consequence of the experiment. These alterations 
of rate were produced in each case immediately after the den- 
sity of the air was changed. 
Adopting the last mentioned rate as a standard, the time- 
keeper was next submitted, during four days, to a pres- 
sure denoted by 25 inches of the mercurial column, when 
its rate was immediately changed from — 6 ". 3 to — 2". 2, 
being an increment of 4".i. By farther diminishing the den- 
sity to a quantity represented by 10 inches of quicksilver, 
the average of a like period gave a rate of -f- 2". 7, being 
another increment of 4". 9 ; and on again exhausting the air 
till the mercury was depressed to 5 inches, the mean of four 
days produced a rate of -f- 4 f, . 6 , being a third increment of 
i /f .9 ; and by restoring the chronometer to the ordinary pres- 
sure of the atmosphere, an immediate change in its rate took 
place ; the mean of ten days producing an average of — 5 ". 9 , 
the close approximation of which to its former detached rate 
being remarkable. 
The results of the preceding experiments are entered for 
the purpose of a more convenient reference in the succeeding 
tables ; together with the average heights of the barometer 
during the times the detached rates were determined ; and 
also the mean temperatures through the entire series of 
observations. 
