ON CHEMISTRY. 
151 
facts, for they are of stupendous moment. There are, as might he 
expected, a great variety of opinions concerning the comparative 
quantity of watery vapour in the atmosphere: at fifty degrees, Davy 
states it to be about ^ of the bulk of the whole, but as the 
specific gravity of vapour is to that of air as ten is to fifteen, the 
weight of vapour is only part. The average temperature of 
day and night throughout the year, may perhaps somewhat exceed 
fifty degrees; therefore, if w 7 e admit that a greater volume of vapour 
is raised during a warm state of the atmosphere than when the 
temperature is low, we may suppose that the quantity exceeds, upon 
an average, that above noted. Some, however, have considered one 
part in one hundred to be a fair estimate of the amount of vapour 
held in solution, or that it varies from to part. 
The subject involves phenomena of far greater moment: it points 
to the origin and source of the atmosphere itself. Whence was the 
aerial volume derived, and what supports and renews it ? for the 
consumption or degradation of the fluid by the processes of animal 
respiration, and natural fermentation are of enormous extent! 
Dr. Priestley and Sir Humphrey Davy, at periods very remote in 
point of time, witnessed phenomena in regard to azot nitrogen, 
which gave reason to suppose that, that gas was not simple, or un¬ 
compounded in its nature. The latter chemist conjectured in fact, 
that he had decomposed it, and that it might be an oxide of hydro¬ 
gen. 
I stated, several years past, that I believed this to be the fact; and 
I then embodied my ideas in the form of the following atmospheric 
theory. 
“ The atmosphere was originally formed out of, and is daily re¬ 
newed by vapours raised from the surface of the earth and waters, by 
the agency of solar induction and decomposition; that it is there¬ 
fore, composed of the elements of w r ater in a new and peculiar ar¬ 
rangement, effected by the energy of specific electro-chemical agen- 
cies. 
I believe that the idea of the aqueous origin of air was once enter¬ 
tained ; but that it was relinquished as untenable, or silently aban¬ 
doned—to use a familiar phrase—as out of fashion. I claim as my 
own exclusive hypothesis, that of the inductive agency of light in 
this vast process; and I therefore am called upon to state the evi¬ 
dences upon which I ground my opinion. 
The first is afforded by the phenomenon of evaporation. The cx- 
'periments of Dr. Halley, the celebrated astronomer, led him to the 
calculation, that as one cubic inch evaporated from every ten square 
