164 On the Heating-Paiters of Arcturus and a Lyra. [Jan. 13, 



The mean result of the observations on these two nights is 



0°-0198 F. 



as a measure of the heating-effect of Arcturus in raising the temperature 

 of the plate of antimony and bismuth when the heat is condensed by the 

 cbject-glass of 12" 75 inches. 



If the absorption by the object-glass be considered insensible, the direct 

 effect upon the pile would be 



0°-000000685 F. 



I have not yet determined the coefficient of absorption for the object- 

 glass, but if it be provisionally taken at j, the direct heating-effect of Arc- 

 turus 



= U r -0000013r F. 

 The result may be otherwise stated as follows : — That the heat received 

 from Arcturus is sensibly the same as that from the whole face of the cube 

 containing boiling water at vDO yards. 



156*9. August 14. 

 Observations of £ Lyres at S h 3S- G.M.T. 



6 = 15 div. 

 9=686 div. 



Heating-power for 3 Lyrae 



= 1-087X 0-725 — =0-0039 F. 

 (24)* O^o 



Observations were subsequently made of cc Lyrae, but the zero was un- 

 steady ; and as the night advanced clouds appeared, and ultimately inter- 

 rupted the observations. 



1569. August 14. 

 aLyrce. Star on a— star on 0=11 div. 

 1869. August 15. 



The night was very clear, and the air steady, but completely saturated with 

 moisture, at a temperature of about 52°. The mean of fourteen observa- 

 tions of the difference of reading for a Lyrae on a and 0 gave onlv 1 1 divs. 

 I have no doubt but that the small effect here obtained was due principally 

 to the amount of moisture in the air. 



1869. August 25. 

 Observations of a Lyrae-. Xight fine. 

 Mean value of the difference from nine observations was 



0=33 div. 

 9 = 609 div. 

 c=24 inches. 

 .-. heating-power of aLyrae = 0 3 -00SS F. 

 This result is again so much smaller than those obtained from Arcturus, 

 although the observations of Arcturus were made under more unfavourable 

 circumstances with respect to altitude, that I cannot but regard it as a fact 



