35 
The air contained in sea water consists of variable quanti- 
ties of free carbonic acid, oxygen, and nitrogen, and Morren 
and Lewy have shown that the changes in the relative pro- 
portion of these gases depend: — (1) upon alteration of tem- 
perature affecting the relative amounts of the dissolved gases 
in accordance with the laws of gaseous absorption ; and (2) 
upon the variations in intensity of direct and diffused solar 
light, producing a corresponding effect upon the vitality of 
sea plants and animals, and hence altering the composition 
of the dissolved gases. 
Some further experiments by Lewy, on the composition of 
the atmosphere above the Atlantic ocean in the tropics, tend 
to confirm the above supposition of the possible increase in 
carbonic acid in the atmosphere above the sea. In fact, if it 
is possible that the composition of the air above the sea in 
our latitudes can be sensibly altered by this phenomenon of 
the variation in the nature of the gases in solution in sea 
water, as Lewy and Morren assert, we might expect that the 
atmosphere above the tropical oceans would manifest to a 
much larger extent variations in the relative amounts of 
carbonic acid and oxygen, since infusoria exist, as is well 
known, in enormous quantities in these oceans, and the 
composition of the air in their waters must necessarily 
undergo rapid variation, and a considerable evolution of the 
dissolved gases must consequently occur. At the instance 
of the French Academy Lewy collected air at different 
times during a voyage from Havre to Santa Marta, and 
on subsequent analysis not only did it appear that the 
mean quantity of carbonic acid was sensibly greater in the 
air of the Atlantic ocean in the tropics than in the air of the 
land, but also that the air of the day was appreciably richer 
in carbonic acid and oxygen than air collected in the night. 
On comparing the means of each series we have, in 10,000 
volumes of air, for the 
