220 Mr. J. Croll on the supposed greater Loss of Heat 



It will be seen that in the first and fourth trials there is a 

 greater consumption of material in the light than in the dark, 

 and in the second and third trials the consumption is greater in 

 the dark than in the light ; but in any case the difference is so 

 small, amounting only to from 2 to 7 grains per hour, that it 

 may fairly be referred to accidental circumstances, such as differ- 

 ences in temperature, in currents of air, and in the composition 

 and make of the candles, the final conclusion to which I am led 

 being that the direct light of the sun or the diffused light of day 

 has no action on the rate of burning, or in retarding the com- 

 bustion of an ordinary candle. 



Hig-hgate, N., 

 July 1869. 



XXVI. On the Opinion that the Souther?! Hemisphere loses by 

 Radiation more Heat than the Northern, and the supposed Influ- 

 ence that this has on Climate. By James Croll, of the Geo- 

 logical Survey of Scotland*. 



THE total amount of heat received from the sun between 

 the two equinoxes is the same in both halves of the year, 

 whatever the eccentricity of the earth's orbit may be. For ex- 

 ample, whatever extra heat the southern hemisphere may at pre- 

 sent receive from the sun during its summer months owing to 

 greater proximity to the sun, is exactly compensated by a cor- 

 responding loss arising from the shortness of the season ; and, 

 on the other hand, whatever deficiency of heat we in the northern 

 hemisphere may at present have during our summer half year 

 in consequence of the earth's distance from the sun, is also ex- 

 actly compensated by a corresponding length of season. 



But the surface-temperature of our globe depends as much 

 upon the amount of heat radiated into space as upon the amount 

 derived from the sun, and it has been thought by some that this 

 compensating principle holds only true in regard to the heat 

 directly received from the sun. In the case of the heat lost by 

 radiation the reverse is supposed to take place. The southern 

 hemisphere, it is asserted, has not only a colder winter than 

 the northern in consequence of the sun's greater distance, but 

 it has also a longer winter; and this extra loss of heat from 

 radiation is not compensated by its nearness to the sun du- 

 ring summer months, for it gains no additional heat from its 

 proximity. And on the same principle our winter in the north- 

 ern hemisphere, owing to the less distance of the sun, is not only 

 warmer than that of the southern hemisphere, but is also at 



* Communicated bv the Author. 



