444 GEOLOGY. 



essentially complete suspension of the formation of sea-ice may be 

 assumed with much reason. Obviously, the succession of such gla- 

 ciations and deglaciations could only continue so long as the general 

 conditions that brought on the glaciation continued to prevail. So 

 soon as they passed away, the oscillating series ceased. 



This hypothesis is dependent on the efficiency of carbon dioxide 

 and water-vapor as thermal absorbents. While this is conceded for 

 the water- vapor, and measurably for the carbon dioxide, the quantita- 

 tive efficiency of the latter has been questioned. This has been touched 

 upon in the Permian discussion, and it will only be added here, that 

 if a lowering of the average temperature of the globe from 5° to 8° C. 

 below the present temperature would be sufficient to produce the general 

 conditions of glaciation, as has been estimated, a direct efficiency of car- 

 bon dioxide to the extent of 1° or 2° C, with the cooperation of the 

 water- vapor and accessory agencies, would probably produce the requisite 

 effects. In the Sahara, the lowness of the moisture in the air often 

 permits the temperature to fall from mid-day heat to 0° C , during the 

 night. If there were no atmosphere at all above the Sahara, the tem- 

 perature would undoubtedly fall 100° to 200° C. more during the 

 night. That it does not do so is due to the efficiency of the remaining 

 constituents of the atmosphere. Their value as cooperating factors - 

 has been greatly underestimated. By mathematical computations, 

 based on Langley's observations on the heat received from the moon, 

 Arrhenius some time since deduced a much higher estimate of the thermal 

 efficiency of the carbon dioxide of the atmosphere than the glacial prob- 

 lem seems to require. 1 More recent experimental determinations give 

 notably lower results. The later results of Arrhenius 2 himself seem 

 still to be more than sufficiently high, while those of Rubens and 

 Aschkinass 3 and of Angstrom 4 do not seem fatally low, though they 

 have been so interpreted. 



Objection has been made to the sufficiency of the consumption of 

 carbon dioxide to produce the effects assigned rapidly enough to meet 

 the requirements of the case, on the ground that the tendency to equilib- 



1 On the influence of carbonic acid in the air upon the temperature of the ground. 

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



2 Kosmische Physik, II, p. 503. 



3 Ann. Phys. u. Chem., 1898, p. 598. 



4 Ibid., 1900, p, 321. 



