426 



must involve the absorption of a corresponding part of the 

 atmospheric carbonic acid. If such a decline in the mean 

 temperature of the earth could take place in a few years, a 

 perceptible tension-difference between the atmosphere and the 

 sea would of course arise, and the results of the above- 

 mentioned general investigation of the state of equilibrium 

 might be seriously vitiated. Nothing of the kind need however 

 be feared. The tension-differences which may arise in this 

 way are very much below the reach of onr analytical methods M- 

 In 1896 Arrhenids^) propounded the hypothesis that the 

 surface-temperature of thje earth depends to a large extent 

 upon the heat-absorbing power of the atmospheric carbonic 

 acid. Taking as his base a series of determinations, published 

 by Langley, of the radiating heat received from the moon, he 

 endeavoured to And out by elaborate calculations, the details 

 of which I must confess myself unable to follow, the heat- 

 absorbing powers of the atmospheric water-vapour and carbonic 

 acid and to compute the influence upon the mean temperature 

 of the earth-surface of definite alterations in the percentage of 

 carbonic acid. He arrived at the extremely remarkable conclu- 

 sion that a diminution of the percentage of carbonic acid from 

 about 0.03 to 0.017 would cause a lowering of the temperature 

 of 4° — 5° at the latitude of 40°— 50°, while, on the other hand. 



If the temperature should fall at a constant rate of say O.ooi" pro year, 

 which I consider to be a high estimate, the tension of the sea would 

 decrease yearly at the rate of '/32000 of its present value and '/32000 of 

 the carbonic acid of the atmosphere (= 7.5 x 10' tons) must be absorbed 

 every year in order to maintain a sliding equilibrium. At a tension- 

 difference of 0.001 °/u the ocean will absorb (according to the calculations 

 on p. 422) 3.85 X 10° tons of CO.^, and '/so of this diflerence or 

 0.00002 % will therefore be amply sufficient for the absorption of 

 7.5 X 10' tons and, consequently, for the maintenance of a sliding 

 equilibrium. There is very little chance that we shall ever be able to 

 detect tension-differences of this degree of magnitude. 

 On the Influence of Carbonic Acid in the Air upon the Temperature of 

 the Ground. Phil. Mag. 1896, pp. 237-276. 



