Letts & Bhake— The Carbonic Anhydride of the Atmosphere. 165 
Having quoted Thorpe’s researches on the atmospheric carbonic 
anhydride over the Irish Sea, the Atlantic, and tropical Brazil, in 
support of this, he then mentions Sterry Hunt’s theory (which 
had in the meantime been elaborated by Winchel), and says, 
regarding the extraordinary supplies of carbonic anhydride, which, 
according to that theory, came from interplanetary space :—-—“‘ I see 
no reason for this hypothesis, which I suspect is not in accordance 
with what we know of the constancy in the rate of rotation of the 
earth, all the immense mass of carbonic anhydride scught to be 
accounted for may have come out of the bowels of the earth, 
whence this gas is still being emitted in enormous quantities. 
The difficulty I apprehend les in the other direction. Our 
atmosphere would long have become unfit for respiration if 
the volcanic carbonic anhydride were not constantly being 
removed by the bases of disintegrating silicates, chiefly as car- 
bonate of lime, of which a considerable proportion goes down 
the rivers into the ocean. This latter will ‘soon’ (in the 
geologist’s sense) have arrived at a state of saturation in regard 
to this component.” 
Dittmar’s views thus coincide with our own up toa certain 
point; but we have gone a step further, and show how “ the state 
of saturation ”’ he speaks of is being checked. 
As regards the actual amount of carbonic anhydride present in 
the atmosphere, we have in the following table collected the results 
of all the more important work which has been done on the subject 
since it first received attention, and these we have arranged in 
chronological order. The table contains the work of some fifty 
observers, and embraces several thousand determinations. All the 
results have been verified as far as possible from the original 
memoirs. In some cases it was necessary to compile them from 
the authors’ figures, which we have done on our own responsibility. 
As regards the columns headed “ Variations,” we have followed 
Wollny’s example. The absolute variation is the difference 
between the maximum and minimum amount of each observer, 
while the percentage variation refers to the ratio of the minimum 
to this excess. 
