and its Influence on Climate. 



431 



cording to Mr. Meech*, if 365*24 thermal days represent the 

 present total annual quantity of heat received at the equator from 

 the sun, 151*59 thermal days will represent the quantity re- 

 ceived at the poles. Adopting his method of calculation, it turns 

 out that when the obliquity of the ecliptic is at its maximum, 

 viz. at 24° 50' 34", the quantity received at the equator would 

 be 363*51 thermal days, and at the poles 160*04 thermal days. 

 The equator would therefore receive 1*73 thermal days less heat, 

 and the poles 8*45 thermal days more heat than at present. 



Annual Amount of Sun's Heat. 



Amount in 1801. 

 Obliquity 23° 28'. 



Amount at 



maximum, 



24° 50' 34". 



Difference. 



Latitude. 

 

 40 

 70 

 80 

 90 



Thermal days. 

 365-24 

 288-55 

 173-04 

 156-63 

 15159 



Thermal days. 

 363-51 

 288-32 

 17914 

 164-63 

 160-04 



Thermal days. 

 -1-73 

 -0-23 

 + 6-10 

 +8-00 

 + 8-45 



When the obliquity -was at a maximum, the poles would there- 

 fore be receiving 19 rays for every 18 they are receiving at pre- 

 sent. The poles would then be receiving nearly as much heat 

 as latitude 76° is receiving at present. 



The increase of obliquity would not sensibly affect the polar 

 winter. It is true that it would slightly increase the breadth of 

 the frigid zone ; but the length of the winter at the poles would 

 remain unaffected. After the sun disappears below the horizon 

 his rays are completely cut off, so that a further descent of 

 1° 22' 34" would make no material difference whatever in the 

 climate. In the temperate regions the sun's altitude at the 

 winter solstice would be 1° 22' 34" less than at present. This 

 would slightly increase the cold of winter in those regions. But 

 the increase in the amount of heat received by the polar regions 

 would materially affect the condition of the polar summer. 

 What, then, is the rise of temperature at the poles which would 

 result from the increase of 8*45 thermal days in the total amount 

 received from the sun ? 



An increase of 8*45 thermal days, or ^ 8 of the total quan- 

 tity received from the sun, according to the mode of calculation 

 adopted in a former paper f, would produce, all other things 

 being equal, a rise in the mean annual temperature equal to 14° 

 or 15°. 



* Smithsonian Contributions to Knowledge, vol. ix. 



t Phil. Mag. for February 1867. Lyell's ' Principles,' vol. i. p. 294. 



