THE VOYAGE OF H.M.S. CHALLENGER. 
»).».) 
my opinion, is not that deep sea-water contains any abnormal proportion of loose or free 
. ib.iuic aeiil (Buchanan’s analyses tend to prove the erroneousness of such a presump- 
tion), but the fact that even alkaline sea-water, if given sufficient time, will take up 
carbonate of lime in addition to what it already contains. The Foraminiferal shells 
disappear at great depths, because it took them so long to reach these depths they had 
time to pass into solution. 
1 had just completed this part of my Summary, when I found in the Chemical 
Xcw>* an interesting article by Alexander Winchell, who, following up certain researches 
of Storry Hunt and Ebelmen, arrives at the conclusion that the immense quantity of 
carbonic acid which must have served for the formation of the deposits of coal and of 
limestone (amounting as it docs to far more than the quantity of carbonic acid which 
would be yielded by the whole of the oxygen now present in the atmosphere), cannot be 
a< counted for otherwise than by assuming that it must have come in from interplanetary 
space. The atmosphere with Winchell, in fact, is nothing but that part of the general 
atmosphere of the universe which our planet has, in the course of time, attracted towards 
itself. I see no necessity 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 acid sought 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, lies in the other direction. Our atmosphere would long have become 
unfit for respiration, if the volcanic carbonic acid were not constantly being removed 
by the bases of disintegrating silicates, chiefly as carbonate of lime, of which a consider- 
able portion goes down the rivers into the ocean. The latter will “soon” (in the geo- 
logist’s sense) have arrived at a state of saturation in regard to this component. 
Absorbed Nitrogen and Oxygen. 
From the carbonic acid in ocean-water, it is an easy transition to pass to the absorbed 
nitrogen and oxygen whieh must prevade the whole of the ocean, because its surface is in 
contact everywhere with the atmosphere. The composition of the latter, in reference to 
it - two principal components, is substantially the same in all its parts, the two gases 
eing a ■■ ited in very nearly the ratio of 21 volumes of oxygen to 79 volumes 
of nitrogen. Jolly, it is true, in a long series of analyses of the air collected at a station 
Munich, made out that the percentage of oxygen (in the air freed of its carbonic acid 
and water) varies with the seasons and the direction of the wind, as shown by the 
mllowiug table which I borrow from Landolt and Bcirnstein’s Physikalisch-chemische 
I'.iIh 11. n. The original is in Wiedemann’s Annalcn der Physik, ser. 2, vol. vi. p. 520. 
* Original in &Mtt, December 2S, 1863, vol. ii. p. 820. For Storry lIunt'B papers we are referred by the author 
to the Amtr. Joum. of Sri. and Art*, May 1880, and other publications. 
