34 CHAMBERLIN— A POSSIBLE REVERSAL [April 1 8 



perature-range on the earth's surface is sixteen times as great as 

 this, while that affecting the solar family is at least sixty times as 

 great. For a hundred million years, more or less, this narrow range 

 of temperature has been maintained quite without break of con- 

 tinuity, unless geologists and biologists are altogether in error in 

 their inductions. On the further maintenance of this continuity 

 hang future interests of transcendent moment. 



So too the maintenance of a narrow range of atmospheric con- 

 stitution, notably in the critical element carbon dioxide, has been 

 equally indispensable. These two critical limitations of temperature 

 and of constitution seem also to have been interdependently corre- 

 lated with one another. 



The climatic problem is as difficult as it is important. The fac- 

 tors are so many, so elusive, so imperfectly determined, perhaps 

 even so imperfectly determinable, that the utmost patience and assi- 

 duity are a duty of the investigator, and the utmost charity of judg- 

 ment an obligation of fellow scientists. I am persuaded, however, 

 that tentative analyses of the tangle of factors are an indispensable 

 aid to the future solution of the problem. One of the gravest diffi- 

 culties confronting us to-day is the imperfection of observations and 

 the inconclusiveness of experimentation ; and this arises in no small 

 degree from the lack of such patient preliminary analyses of the 

 problem as shall bring into sharp recognition the occult things that 

 are to be observed and the precise experimental determinations 

 which alone can really aid in the solution. If the little contribu- 

 tion of this half hour shall have any value at all, it will lie in its 

 suggestive relations to the larger problem of secular climates, past 

 and prospective. 



As this larger problem has recently assumed, with some of us, 

 a phase much at variance with its more familiar aspects, it may need 

 to be briefly sketched. It has been customary to assign to the primi- 

 tive earth a climate quite beyond the Miltonian conception of 

 Gehenna in its fiery intensity, and to predict an impending refrig- 

 eration scarcely inferior in antithetic supremacy. The familiar con- 

 ception of the sum-total of atmospheric history as a decline from 

 one excess to another as the sequence of thermal wastage, is a 

 logical deduction from the hypothetical derivation of the earth from 



