396 Intelligence and Miscellaneous Articles, 



strate, starting from the fundamental equation 





that, if the effective temperature cc of the sun is sufficiently elevated 

 for a variation of 250° in the temperature t of the enclosure not to 

 affect the quantity of the excess d—t, the constant value of the 

 excess must be infinitely greater than any of those which have been 

 observed. Putting aside the hypothesis of cc= oo, the equation 

 above recalled shows that d — t must diminish continuously in pro- 

 portion as the temperature of the enceinte rises, the law of this 

 diminution being represented by the formula 



where c is a constant the value of which is proportional to the in- 

 tensity «* of the radiation at the time of the experiment. 



This diminution of 6 — t with the rise of the temperature of the 

 enceinte has been verified in the experiments which I have made 

 with a large actinometer constructed essentially like the small one 

 described in my last communication, with only the modifications 

 necessary in order to operate at a high temperature. This is shown 

 by the following Table, in which I have also inscribed the values of 

 ax and oo deduced from each observation by the method of calcula- 

 tion previously explained. 











Corrected 











e. 



t. 



e-t. 



excess of 

 cooling. 



**. 



X, 





h m 



o 



o 



o 







1407 



Aug. 12. ... 



1 



11010 9935 1075 



1618 



49100 



„ 31.... 



1 45 



11695 107-40 9-55 



1417 



45700 



1399 



i Sept. 5.... 



1 10 



125-40 116-15 925 



13-79 



47600 



1404 



lAug. 26. ... 



1 



1U-72 136-50J 8-22 



1215 



48910 



1408 



II. Experiments made at divers altitudes have led me to repre- 

 sent the intensity a r , of the solar radiation enfeebled by its passage 

 through our atmosphere, by 



r x K+bf 

 cos z 



a x being the true intensity of the solar radiation before passing 

 through our atmosphere, H the atmospheric pressure at the place 

 of the experiment, / the value, in millimetres, of the actual tension 

 of the aqueous vapour, z the zenith-distance of the sun, p and b con- 

 stants, p=0-9989, and 6=7*8. 



The following Table exhibits the accordance of the formula with 

 experiment. The last column contains the values of oc deduced 

 directly from observation ; the penultimate column gives the values 



