158 



LIFE ON THE EAETH. 



for each zone of latitude to be an increase of warmth 

 proportioned to the difference of area between that 

 zone and the equatorial zone. On this supposition 

 the following calculation is made 1 . 



The addition to mean temperature in lat. 60 

 being taken at 30, the scale of augmentations for the 

 whole series of latitudes will be nearly as in Col. I., 

 and, the equatorial temperature remaining the same, 

 the temperature for each latitude up to 70 will be as 

 in Col. II. 



These temperatures would meet the geological 

 requirement; but it seems very doubtful whether 

 there is enough of probability about the hypotheses 

 on which they are founded, to meet the two objec- 

 tions which follow. 1. The augmentation, here attri- 



1 The formula is merely this. Augmentation = A (rad. cos. 

 lat.). 



