The Earl of Uosse on the Radiation of Heat from the Moon. 317 

 where e = ?r — apparent distance between the centres of the sun and 

 When e=0 (full moon), Q= — . n, 



7T C 



when e=-(half moon), Q= -, 



when e = 7r (new moon), Q = ; 

 .*. if full moon = 100, Q in general 



= 100(l — -cose + sin e^ (a) 



In column 6 we have the deviation for full moon calculated from 

 the observed mean deviation for each night. 



In column 7 the supplement of the apparent distance between the 

 centres of the sun and moon. 



In column 8 the approximate mean altitude of the moon. 



In column 9 the number of times the telescope was put on or off 

 the moon during the observations included in the mean result. 



In all these observations the deviations which have been measured 

 are those due to the difference between the radiation from a circle of 

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

 sky close to it not containing the moon's disk. 



The annexed diagram will show approximately the rate at which 

 the moon's light increases and diminishes with its phases as deduced 

 from formula (a) ; and the ringed dots with the accompanying Roman 

 figures (for reference) give the quantity of the moon's heat as deter- 

 mined by observation on different nights. 



Although there is considerable discordance between some of the 

 observed and calculated quantities of heat, the results suggest to us 

 that the law of variation of the moon's heat will probably be found 

 not to differ much from that of the moon's light. It therefore follows 

 that not more than a small part of the moon's heat can come from 

 the first of the three sources already mentioned. 



With the view of ascertaining what proportion of the sun's heat 

 does not leave the moon's surface until after it has been absorbed, 

 some readings of the galvanometer were taken on four different 

 nights near the time of full moon, with a disk of thin plate glass in 

 front of the face of each pile ; and the deviation was about six or 

 eight divisions. 



As the glass screens were examined with care for dew after re- 

 moval on each night, and none was perceived except on one occasion, 

 the probable percentage of the moon's heat which passes through plate 

 glass is 8, or rather less. 



Few experiments appear to have been made on the absorptive power 

 of glass for the sun's rays ; but, from the best data that I have been 

 able to obtain, I find that probably about 80 per cent, pass through 

 glass. 



The greater part of the moon's heat which reaches the earth ap- 

 pears, therefore, to have been first absorbed by the lunar surface. 



from an element (<5S) of the moon's surface =K . 5S . cos . cos <p, 9 and <p being 

 respectively the inclinations of the lines to the sun and to the earth from the 

 normal to that point of the moon's surface, and K a constant. 



