146 



Marvels of the Universe 



Lunar topography differs essentially from that of the earth, ^\'hile on this planet the higher 

 masses of the crust are arranged in mountain chains, upon the moon they always take a circular 

 form, from the outlines of the greatest " seas " to the smallest craters. To explain this 

 characteristic configuration we must remember that the lunar soil, as it became colder and 

 solidified, enclosed a considerable quantity of vapour and gases. These gases, seeking an escape 

 from the interior, have brought great pressure to bear on the exterior surface of the moon. One 

 can perceive evidences of these forces with the naked eye, but it is possible by means of photo- 

 graphs of the full moon to examine them in the long white tracks which spread out from the 

 mountain of Tycho, and which appear especially brilliant. These white tracks seem to have been 



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PLATO 



The large crater-ring on the right hand of the picture is that of Plato, Within this vast district other craters have appeared 

 and passed away, or. as is sometimes the case, have changed their position, and these phenomena support the belief that Ml the 

 craters on the Moon are not yet extinct. 



fissures across which floods of light-coloured lava have flowed, filling up the crevasses and solidi- 

 fying. As for the mighty circles, it is possible that they were gas bubbles which rose to the 

 surface and broke, producing a complete circular depression. The greatest formations must be 

 the most ancient, the extent of the disturbed surface diminishing as the expansive force of 

 the gases gradually lessened. The truly colossal dimensions of several of the circles and their 

 surrounding heights give an idea of the forces which were in action in primitive times ; the gaping 

 mouth of Tycho measures about 52 miles and 1.435.8 yards in diameter, and the ramparts attain 

 a height of about 3 miles and 552.7 yards. The circle of Clavius is 130J miles wide, and has an 

 elevation of 4 miles 615.4 yards. One can count upon the moon's surface about twenty circles 

 whose diameter exceeds 60 miles, and about as many peaks of a greater height than Mont Blanc ; 



