12 The Earl of Rosse on Lunar- Heat Radiation. [June 16, 



Anml ,£4-1-, 



April i otn 

 April 20th 



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Altitude 

 of part 

 of sky- 

 examined. 



Calculated 

 difference 

 of tem- 

 perature. 



Tempera- 

 ture of tin 

 ressel. 



Apparent 

 tempera- 

 ture of 

 the sky. 



Kemarks. 







49 



49 



*3h 



5o 



64 



64 







23-9 



3 2 *7 

 28-3 

 28-3 



3o'i 

 262 







55*5 



49 



5* 



5°-5 



47 



44 







31 



16- 3 



22*7 

 22*2 

 l6"9 



17- 8 



} 



Sky hazy. 



Sky apparently black 

 and transparent ; 

 occasional light 

 clouds. 



If the temperature of space be really as low as is supposed, this result 

 seems to indicate considerable opacity of our atmosphere for heat-rays of 

 low refrangibility. 



The ever varying transparency of our atmosphere has been found to be 

 a very serious obstacle ; but the much greater steadiness of the needle 

 during the later experiments (the mean error of the last few nights' ob- 

 servations having been from two to three and a half per cent, only of the 

 whole deviation*) encourages us with the hope that, by taking advantage 

 of favourable moments, and measuring the moon's light simultaneously 

 with her heat, more accurate information on this subject may soon be 

 acquired. 



The observations were examined with the view of ascertaining how far 

 the heating-power of the moon's rays varies with her altitude. Owing to 

 the interference of clouds, and the limited range of altitude within which 

 the observations were made, it is hardly worth while to give the results in 

 detail ; however, I may just say that the heating-power of the moon's rays 

 appears to diminish with her altitude only about one-third as fast as the 

 intensity of the solar chemical rays, as ascertained by Roscoe and Thorpe. 



An attempt was made to ascertain, by comparing two measurements of 

 the moon's light at different altitudes with two corresponding measure- 

 ments of her heat, whether our atmosphere intercepts the heat-vnys to a 

 greater extent than the luminous rays. It was found that while the light 

 was diminished with the altitude in the proportion of about 3 to 1, the 

 heat was diminished in the proportion of about 5 to 1 . In consequence, 

 however, of much of the moon's light and heat being intercepted by hazy 

 clouds, or condensed vapour, at the lower altitude, the experiment was in- 

 conclusive as to the effect of a transparent atmosphere on the dark rays 

 of heat. 



The accompanying diagram shows the proportion between the amount 

 of lunar heat found on various nights at various ages of the moon. There 

 appears to be a general accordance between the variation of her radiant 

 heat with her phase and the corresponding amount of her light as deduced 

 by calculation. 



* During the experiments of the previous season the mean error varied between 27 

 per cent, and 85 per cent, or more. 



