September 1, 1893.] 



KNOWLEDGE 



169 



THE GREAT ILUNAR CRATER COPERNICUS. 



By A. C. Ran YARD. 



THE scale of the lunar craters, as compared with the 

 little planet on which they are found, will probably 

 be best realized by a comparison with terrestrial 

 objects. If the moon could be cut in half, and 

 one of its hemispheres placed upon the earth's 

 surface without altering its shape, it would form a dome- 

 shaped mountain about a thousand and eighty miles high, 

 the circular base of which would about correspond in size 

 with the western hump of Africa comprised between the 

 Gulf of Guinea on the south and Morocco and Algiers on 

 the north. 



The great crater Copernicus, the photograph of which 

 we are about to examine, is fifty-five miles in diameter ; so 

 that if London were situated upon its southern edge, 

 Cambridge would lie within its northern border. This 

 great ci-ater is only the central region of a district more 

 than five hundred miles in diameter which was evidently 

 violently disturbed by the forces that built up the central 

 ring ; for stretching in all directions around the crater will 

 be noticed a series of curiously curved and branching 

 whitish rays, the connection of which with the crater as a 

 centre is unmistakable, although they do not radiate from 

 it in straight lines like the streaks diverging from the 

 crater of Tycho. 



Copernicus, in spite of its 

 gigantic size, presents many 

 analogies to terrestrial vol- 

 canoes. It is not quite circular 

 in outline, but the craters of 

 many terrestrial volcanoes 

 are not circular, and are 

 sometimes distinctly poly- 

 gonal. In Plate I. a string 

 of little craters will be 

 noticed on the western slope 

 of Copernicus, midway be- 

 tween the great crater and 

 Eratosthenes (110). 



Many similar strings of 

 little craters are found around terrestrial volcanoes, 

 usually marking a line of fissure which can sometimes 

 be distinctly traced. Thus Prof. Judd, in his book on 

 "Volcanoes" in the International Science series, states 

 that dui-ing the eruption of Etna in 1865 a line of 

 eight scoria cones formed along a fissure on the flanks of 

 Etna. Similar lines of craters have at times formed on the 

 sides of Vesu\ius, and a study of the sections of volcanoes 

 dissected by denudation affords convincing evidence that 

 volcanic cones generally 

 originate upon lines of 

 fissure. The string of 

 little craters between 

 Eratosthenes and Co- 

 pernicus should be exa- 

 mined with a magnify- 

 ing-glass ; they are best 

 seen on Plate I. , but can 

 be traced on Plate II., 

 though a photographic 

 defect in this plate partly ^"^- ^■-'^^'' ^"°*'' Carpathians, 

 obliterates the crater of Eratosthenes. Two strings of 

 smaller craters may be traced branching from the main 

 stream, which extends along the flank of Copernicus for a 

 distance of more than one hundred miles, and then crosses 

 the Apennines in a valley or gap between Eratosthenes and 

 the rugged range of the Carpathians which lies to the 



Fig. 1. — Copernicus at .Sunris 



north of Copernicus. After crossing the Apennines it 



debouches on to the Mare Imbrium at the 



head of a curving white ray, or lava stream, 



that runs for more than three hundred 



miles over the Mare Imbrium, reaching 



far beyond the 



craters Timo- 



charis (121) and 



Lambert (122). 

 The question 



whether this 



whitish curving 



ray and the other 



similar rays 



which radiate 



from Copernicus 



correspond to 



streams of liquid 



matter which 



once flowed from 



the crater, or 



whether they are mere discolorations of 



the surface which follow the course of 



Fig. 3.— Kay from figgures in the lunar crust, is one of very 



opermcus. g^gat interest, and I would in\'ite the reader 



to spend a few minutes in carefully examining the course 



Fig. 4. — Eratosthenes, and 

 streaks from Copernicus. 



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