188 



Mr. J. Croll on Ocean-currents in relation to the 



The temperature of a place, other things being equal, is pro- 

 portionate to the quantity of heat received from the sun. If 

 Greenland receives per given surface as much heat from the sun 

 as England, its temperature ought to be as high as that of Eng- 

 land. Now from May 10 till August 3, a period of eighty-five 

 days, the quanity of heat received from the sun in consequence 

 of his remaining above the horizon is actually greater at the 

 north pole than at the equator. 



Column II. of the following Table, calculated by Mr. Meech*, 

 represents the quantity of heat received from the sun on the 

 15th of June at every 10° of latitude. To simplify the Table, 

 I have taken 100 as the unit quantity received at the equator on 

 that day instead of the unit adopted by Mr. Meech : — 





I. 



II. 



III. 





Latitude. 



Quantity of 



June 







beat. 



temperature. 



Equator 



o 







100 



80°-0 





10 



111 



811 





20 



118 



81-1 





30 



123 



773 





40 



125 



680 





50 



125 



58-8 





60 



123 



51-4 





70 



127 



39 2 





80 



133 



30-2 



North pole... 



90 



136 



274 



The calculations, of course, are made upon the supposition that 

 the quantity of rays cut off in passing through the atmosphere 

 is the same at the poles as at the equator, which, of course, is 

 not exactly the case. But, notwithstanding the extra loss of 

 solar heat in high latitudes from the greater amount of rays cut 

 off, still, if the temperature of the arctic summers were anything 

 like proportionate to the quantity of heat received from the sun, 

 it ought to be very much higher than it actually is. Column III. 

 represents the actual mean June temperature, according to Prof. 

 Dove, at the corresponding latitudes. A comparison of these two 

 columns will show the very great deficiency of temperature in 

 high latitudes during summer. At the equator, for example, the 

 quantity of heat received is represented by 100 and the tempe- 

 rature 80°; while at the pole the temperature is only 27°'4, 

 although the amount of heat received is 136. This low tempe- 

 rature during summer, from what has been already shown, is due 

 chiefly to the presence of snow and ice. If by some means or 



* See 'Report of Smithsonian Institution' for 1856, p. 330, Smith- 

 sonian Contributions, vol. ix. 



