370 RELATIVE ATTRACTIONS OF 
dered to be supported by the circumstance of a 
vacuum, to which water is exposed, becoming in- 
stantaneously saturated with vapour, whilst dry 
air, on being exposed to water, is a comparatively 
long time over becoming saturated ; together with 
the supposed fact, that space, whether full or void 
of air, is capable of retaining the same quantity 
of vapour, while the temperature remains the 
same. However tenable this reason may be as 
regards evaporation from water, something further 
seems to claim our adoption in regard to the eva- 
poration of water from diluted sulphuric acid ; 
for, if the vis inerive of the particles of air be the 
sole cause of the retardation, evaporation, though 
more slow in air than in vacuo, should go on until 
as much water has left the acid as would leave it 
in vacuo of the same dryness and at the same 
temperature,—which does not accord with expe- 
riment. 
From the results of my experiments, it appears 
to me unavoidable that we should adopt the no- 
tion that the weight of the atmosphere is the true 
cause of the retardation :—it has, however, been 
asserted, that if the weight was the cause, it 
would effectually prevent any vapour from arising 
from water below the temperature of 212°; but, 
