154 MR. T. E. THORPE ON THE AMOUNT OF CARBONIC ACID 



light on tlie microscopic animalcula which, according to 

 Ehrenbergj are always present in sea-water — basing their 

 conclusions on the examination of the water left by the 

 recession of the tide in the hollows of the rocks or shore, 

 in which infusoria develope with great rapidity, and in 

 which consequently under favourable circumstances, all 

 these phenomena are eminently exhibited. 



If it is possible that the composition of the air above the 

 sea in our latitude can be sensibly altered by this pheno- 

 menon of the variation in the nature of the gases in solu- 

 tion in sea-water, it is reasonable to expect that the atmo- 

 sphere 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 weU known, in 

 enormous quantities in these oceans, and the composition 

 of the air in their waters must necessarily undergo rapid 

 variation, and a consequent evolution of the dissolved 

 gases occur. Some experiments by Lewy on the com- 

 position of the air of the Atlantic Ocean (Ann. de Chimie 

 et de Phys. xxxiv. 14) tend to confirm this opinion. At the 

 instance of the French Academy, Lewy collected air at 

 different times during a voyage from Havre to Santa Marta. 

 On subsequent analysis, the air collected during the day 

 appeared to be sensibly 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 day The night 



(mean of 7 expts.). (4 expts.). 



Carbonic acid 5*299 3'459 



Oxygen 2105-801 2097"4i2 



This variation appeared to increase in proportion as the 

 middle of the ocean was approached ; and in air collected 

 on December i8th, 1847, at about equal distances from 

 Africa and America, the widest difference was observed : — - 



