374 Royal Society : — 



The experiment made during the previous season to determine the 

 ratio between the heating-power of the moon and of the sun was 

 repeated with more care ; and the value found, taking what appeared 

 to be the most probable mean heating-power of full moon, as deter- 

 mined on various nights, was 



Sun's total heat _oo^aa 

 Moon's total heat 



Taking the percentage of light transmitted by glass* = 92 

 Do. do. of sun's heat =87 



Do. do. of moon's heat =12 



Do. do. of heat from a body at 180° F. = 1-C 



If - — - and — — represent respectively the percentage of dark 



U ~p ' U "T" ' 



and luminous rays present in the moon's radiant heat, and n , 



and rr, ., the corresponding quantities for the sun's radiant heat, 

 we have 



and 



0X-016 + /X-92 _ , 



Z+o 12 ' 



0'X'016 + /'x-92 



Z' + O' 



= •87; 



••4=o^ x S= 82600x TP= 678300 - 



In all the foregoing experiments on lunar radiation the quantity 

 measured by the thermopile was the difference between the radiation 

 from the circle of sky containing the moon's disk and that from a 

 circle of sky of equal diameter not containing the moon's disk ; we 

 have obtained no information in reference to the absolute temperature 

 of either the moon or the sky. 



The following experiment was therefore made with the view of 

 trying to connect the radiation of the sky with that of a body of known 

 temperature. The deviation due to each degree (Fahrenheit) differ- 

 ence of temperature between a blackened tin vessel containing hot 

 water and subtending a given angle at the pile and a similar vessel 

 containing colder water was first ascertained ; then a similar deter- 

 mination of that due to the difference of radiation from one of these 

 vessels, and from a portion of sky of equal diameter, was made. 

 The following was the result : — 



* All these values, except the first, were determined by experiment for the 

 specimen of glass employed. 



