1873.] On the Radiation of Heat from the Moon. 241 



8. If p be the radius of curvature, 



tan 8 n 



tan 



tan 2 1 



9. Regarding AGr, AH as conjugate diameters, 



sin 2 AH -f sin 2 AG- = sin 2 a + sin 2 b, 

 sin AH . sin GrF = sin a . sin b. 



10. If p be the perpendicular from A on the tangent at Gr, 



tan 2 a tan 2 b 



tan 2 j9 



= tan 2 a + tan 2 b — tan 2 AG-. 



11. tan 2 G-N-tan 2 Z= * sin 2 G-M. 



COS 



12. sin 2 a — sin 2 AGr ] e 2 . 2nM 



• 2 tt a • 2 * r = sm 2 G-M. 



= sm 2 HA — sin 2 b J l— e 2 



Cor. tan 2 GrN = h , (cos 2 AG- - cos 2 a cos 2 b). 



cos^ o sm 2 a 



March 27, 1873. 



Sir GEORGE BIDDELL AIRY, K.C.B., President, in the Chair. 



It was proposed by the Earl of Rosse, and seconded by Dr. Sharpey, — 

 That the best thanks of the Royal Society be given to Dr. Bence 

 Jones for his munificent present of a bust of Earaday. 



The Bakerian Lecture. — C( On the Radiation of Heat from the 

 Moon, the Law of its Absorption by our Atmosphere, and 

 its variation in amount with her Phases/' By the Earl of 

 Rosse, D.C.L., F.R.S., &c. Received February 3, 1873. 



(Abstract.) 



In this paper is given an account of a series of observations made in 

 the Observatory of Birr Castle, in further prosecution of a shorter and 

 less carefully conducted investigation, as regards many details, which 

 forms the subject of two former communications* to the Royal Society. 



The observations were first corrected for change of the moon's distance 

 from the place of observation and change of phase during the continuance 

 of each night's work, and thus a curve, whose ordinates represented the 

 scale-readings (corrected) and whose abscissae represented the corre- 

 sponding altitudes, was obtained for each night's work. By combining 

 * Proceedings of the Eoyal Society, vol. xvii. p. 436, vol. xix. p. 9. 



