144 



Marvels of the Universe 



At this epoch the month and the da}' of the earth and of the moon had a common duration 

 of five hours thirty-six minutes. Our satellite continued to revolve round the mother planet ; 

 gradually, however, getting farther away and lessening the speed of her revolutions. Her surface 

 was troubled by immense tides provoked by the excessive attraction of the earth, which caused the 

 formation of a great bubble. The lunar rotation caused this excrescence to veer round to the east, 

 but the all-powerful attraction of the earth brought the prominence into line with herself. The 

 swelling acted like a bridle upon the daily movement of the moon and caused the speed to relax, until 

 the lunar day became at length equal in duration to the present lunar month. The tides have ceased, 

 suppressed somehow by the action of the earth : but the}' have left the mark of their action in the 

 lengthening of the hemisphere turned towards us, and which gives the moon the shape of an egg. 



I'hoto liu] 



One of the great grey depressions w 

 called seas. The one here shown is th 

 Posidonius and Caquet — which exhibit s 



VIEW ON THE MOON. 



'hich cover a great part of the surface of the Moon 

 ' important Sea of Serenity, possessing on the 

 igns of activity. 



[_T/i(^ JV/-X>?o OlK^ercalori/. 



For want of a better term they are 

 rth-west of its borders two volcanoes — 



So it is that the moon is of terrestrial origin. 



But it is less dense, for although the constituents 



of its mass are those of the terrestrial surface, they have, nevertheless, a density only twice as great 

 as that of water, while the mean density of the earth is five and a half times as great, and in its central 

 depths the latter must attain the density of iron and heavy metals, which brings its total density 

 to at least seven to ten times that of water. Above all, the lunar land surfaces appear to be com- 

 posed of formations of chalk, broken by a vast number of fissures and very light. The extreme 

 brilliancy of their reflections creates the impression that the whole surface is coated with marble 

 or a carbonate of chalk. During the day this reflection is equal to that of the whitest clouds. 



On first thoughts it would seem that a vast atmosphere should envelope this little globe broken 

 off from our own, and that a great deal of vapour would be found thereon. Certainly the moon at 



