102 



G. F. Becker — Certain Astronomical 



from the mean temperature, that the curves representing mean 

 rate afford a sound basis for comparison between continental 

 climates for different values of the eccentricity of the earth's 

 orbit or for different values of obliquity of the ecliptic, the 

 composition of the atmosphere and the intensity of solar radia- 

 tion being supposed constant. This conclusion seems to me 

 fully justified by diagram 2, and it will be assumed in what 

 follows. 



lDO°F 



Figure 2. 



Heat rates for present conditions in each of the great seasons. The rates for 

 zero eccentricity and present obliquity are shown by dotted lines. Points marked 

 X are Asian mean temperatures in January and July. Points marked Y are ^orth 

 American mean temperatures for the same months. 



In considering the effect of secular variations of the earth's 

 orbit on the accumulation of ice, certain criteria of climate 

 must be fixed upon. So far as I can see, the conditions pre- 

 vailing in a glaciated hemisphere should be as follows. The 

 torrid and lower temperate zone, in which evaporation chiefly 

 takes place, should be as warm as is consistent with other con- 

 ditions ; for it must be remembered that the tension of aqueous 



