852 SPECIAL RESULTS IN THE URA.NOLCGICAL 



being nearly j- of the Earth's diameter ; its volume 

 of that of the Earth ; its mass, according to Lindenau, 

 (according to Peters and Schidloffsky, -gV) of the mass of 

 the Earth; and its density 0-619, or almost -fills the den- 

 sity of the Earth. The Moon has no sensible flattening at 

 the poles, but has an extremely small elongation or swelling 

 towards the Earth (the amount of which is determined by 

 theory). The rotation of the Moon round its axis is per- 

 formed (as is probably the case with all satellites in reference 

 to their respective primary planets) in exactly the same time 

 as that in which it completes its revolution round the Earth. 

 The solar light reflected from the surface of the Moon is 

 in every zone fainter than the solar light reflected in the 

 daytime from a white cloud. When taking lunar distances 

 from the Sun for determinations of geographical longitude, 

 it is not unfrequently found difficult to distinguish the 

 Moon's disk among the more intensely illuminated cumuli. 

 On mountains between thirteen and seventeen thousand feet 

 high, where, in the clearer mountain air, only light, feathery 

 cirrous clouds are to be seen, I found it much easier to 

 distinguish the Moon's disk, both because cirrus from its 

 slighter texture reflects less of the Sun's light, and the light 

 of the Moon loses less in passing through thin atmospheric 

 strata. The ratio of the intensity of the Sun's light to that 

 of the full moon deserves a fresh investigation, as Bouguer'* 

 generally received determination (-j-oVo iro ) differs so strik- 

 ingly from the indeed more improbable one of Wollaston 



t i \ (562\ 



V.800000/V /' 



The yellow light of the Moon appears white by day, be- 

 cause the strata of air through which we see it being blue, 

 present the complementary colour to yellow ( 563 ). Accord- 



