364 T. C. CHAM BERLIN 



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 correlated 

 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 assiduity 

 are a duty of the investigator, and the utmost charity of judgment 

 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 difficulties 

 confronting us today is the imperfection of observations and the incon- 

 clusiveness 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 contribution of this paper 

 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 refrigeration scarcely 

 inferior in antithetic severity. The famihar conception 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 a gaseous or quasi- 

 gaseous nebula through gravitative condensation. To some of us, 

 however, such a derivation seems inconsistent with the dynamics of 

 the present solar system, and an alternative hypothesis has been 

 formulated to meet the supposed requirements of existing phenomena. 

 The acceptance of this requires a reconstruction of the whole concep- 

 tion of geologic climates. The new view discards the primitive 

 molten state as a necessary condition, and presents the alternative 

 of a slow growth of the earth by planetesimal accessions. This 



