PORTION OF THE COSMOS. THE PLANETS. 363 



strictest sense of the words, throughout whole lunations 

 in " perpetual light " they are truly " islands of light/' 

 and can be recognised with very low magnifying powers 



(585). 



As exceptions to the generally prevailing lunar type of 

 circular and annular forms, we find, almost in the middle of 

 the northern half of the Moon's disk, some true mountain- 

 chains (Apennines, Caucasus, and Alps). They range 

 nearly from south to north, through almost 32 of latitude, 

 in the form of a very flattened bow a little curved towards 

 the west. Here we see countless mountain ridges, and 

 some exceedingly pointed summits crowded together. Only 

 tt few annular mountains and crater-like depressions (Conon, 

 Hadley, and Calippus) are interspersed, and the whole re- 

 sembles more nearly the conformation of our terrestrial 

 mountain-chains. The lunar Alps, which are inferior in 

 elevation to the lunar Caucasus and Apennines, present 

 a remarkably broad cross valley, which intersects the chain 

 from S.E. to N.W. It is surrounded by summits which 

 surpass in altitude the Peak of Teneriffe. 



A comparison between the elevations on the Moon and 

 on the Earth, viewed relatively to the diameters of the two 

 bodies, gives the remarkable result, that while the satel- 

 lite is four times less than the planet, its highest summits 

 are only 600 toises (3837 Eng. feet) lower than the 

 highest summits of the Earth ; so that the lunar mountains 

 are -^-fr of the Moon's diameter, and the terrestrial 

 mountains -p^Vr of that of the Earth. Of the 1095 

 elevations which have been measured on the Moon, I find 

 39 which arejaigher than Mont Blanc, and 6 above 38000 

 Paris feet (19184 English). The measurements are made 

 either by determining the distance, reckoned from the limit 



