ANNIVERSARY ADDRESS OE THE PRESIDENT. xlvii 



Such, a state appears hardly reconcileable with the existence of 

 the trees and other land-plants which abounded in the Carboniferous 

 period ; and the time which must have since elapsed in cooling down 

 to the extent of 10° is only to be expressed in almost countless 

 millions of years, while some of the phaenomena to be explained 

 belong to the latest or tertiary periods of geology. 



As long as our reasonings on this subject are limited by the con- 

 dition of constancy in the mass and quality of the atmosphere, and in 

 the influence of the sun and ethereal spaces, these objections apply ; 

 but if, further, we consider what must be the effect of an aug- 

 mented surface-heat on the ocean and the atmosphere, we shall see 

 reason to modify this opinion. The oceans, especially deep oceans, 

 would distribute a largely augmented measure of circulating hot 

 water, as well as throw off more aqueous vapour. The winds would 

 be more powerful, and have a greater effect on the ocean-streams, to 

 which always, and in all conditions of the globe, much of the pecu- 

 liarity of local climate beyond the tropics is due. The larger volume 

 of aqueous vapour transferred to the atmosphere in one region would 

 give out, on condensation in another, a larger measure of heat*, and 

 it is conceivable, that with such an atmosphere, operating like extra 

 packing round a steam-pipe, the waste of heat by radiation from the 

 surface of the earth might be reduced. From these causes the sur- 

 face-warming effect of a given determinate flow of heat to the surface 

 of the earth might have been in a higher ratio than that indicated 

 by the intervals of the isothermal surfaces. 



Nor is this the only, or even the principal, argument which may 

 be urged in mitigation of the strict interpretation of the formula. 

 It is manifestly altogether dependent on the identity of the atmo- 

 spheres, not only as to the weight of the vaporous element, but still 

 more on the mass of the gaseous elements. Who is to assure us that 

 the constitution of the atmosphere, which is not a chemical com- 

 pound, but an aerial mixture, is necessarily fixed and constant ? Is 

 it not, on the contrary, most probable that it is variable, both in the 

 proportions of oxygen, nitrogen, and carbonic acid, and in the sum 

 of the whole ? What is it but the gaseous residuum of a planet cooled 

 and solidified, but still for half its weight composed of oxygen 

 capable of emancipation by augmentation of heat and reduction of 

 pressure ? Is not a good part of the history of rocks the history of 

 chemical changes, often characterized by the absorption and conden- 

 sation of oxygen-gas ? Has not the atmosphere lost sensibly of its 

 ancient proportion of carbonic acid, now fixed abundantly in coal, 

 and still more in limestone ? Could we now increase the mass of 

 the atmosphere by only a small fraction, would not the temperature 

 at the earth's surface be sensibly augmented, and the waste of heat 

 by radiation diminished ? 



These considerations appear to me to have weight ; and if the idea 

 of a diminishing atmosphere and a decreasing ocean be unfamiliar, it 

 may perhaps be more readily grasped if we scrutinize the dry sur- 



* The weight of vapour which air is capable of taking up is doubled by an 

 elevation of 2P Fahr. 



