stribution of Heat at the Surface of the Sun. 151 



curve of the intensity of heat, taking as abscissae the parts 

 of the sun's diameter, and as ordinate the intensities them- 

 selves, it appears that this curve (a kind of inverted para- 

 bola) is not symmetrically disposed about the axis of the 

 ordinates, but a good deal inclined towards the upper edge. 

 I subjoin some numbers which represent the intensity of 

 heat in the parts of the diameter of the sun, taken in minutes, 

 + above, and — below the centre of the image. 



Positions on the diameter \ 



of the sun in declina- I + 14'-96 +ll'-32 +3'-00 + 1' 32 -10'-9 -14'-88 



tion, J 



Relative intensity of heat, 57-39 88-81100-00 99-48 81-32 54-34 



These are the results of eight series of experiments, none 

 of which is found in contradiction with the others, and their 

 separate numbers are very nearly the same, so that the fact 

 seems to me completely ascertained. It is certainly curious 

 that the maximum of heat corresponds with the position of 

 the solar equator, as visible from the earth at the epoch of 

 the experiment (20th, 21st, 22d March). This leads natu- 

 rally to the conclusion that the solar equatorial regions must 

 be hotter than the polar regions, as was suspected already 

 from the more frequent appearance of the spots there. The 

 conclusion seems perfectly accurate, even admitting a solar 

 atmosphere, since the effect of this last should be to diminish 

 symmetrically the radiation around the centre of the image ; 

 on the contrary, if the polar regions are less hot than the 

 equatorial, the intensity of heat should have been less in 

 the lower part of the image, where the south pole of the sun 

 was visible ; and consequently, the parts having equal dis- 

 tance from the centre of the image, had a very different 

 heliographical latitude, on account of the inclination of the 

 solar axis to the ecliptic. From these principles only, the 

 non- symmetry of the curve is accounted for. If this alone 

 is the cause, the curve will be found symmetrical in the 

 months of June and December, and reversed in September, 

 since in the two former the equator passes through the centre 

 of the image, and in the last is below it. But it is not im- 

 possible that the two solar hemispheres should possess diffe- 

 rent temperatures, as seems to be the case on the earth, and 

 is suspected in Mars. If this is the case, these researches 



