Lunar Details. 31 



siderable. B. and M. measured it at about 6600 feet; and 

 5500 feet under a doubled angle of illumination, when the end 

 of the shadow would fall in a less depressed part. Schr/s two 

 measures gave about 8000 and 7500 feet. The smaller crater, 

 Menelaus h, lying just S.W. of the larger one, has, according to 

 Schr., a depth of 4570 feet — greater in proportion to its dia- 

 meter, as he always observed with regard to the lesser cavities. 



From one of the " Phases" (No. 9) of Revel's ancient Seleno- 

 graphia, it would appear that some mountains in this vicinity 

 must be of extraordinary height. He makes their projection 

 into the night side, even in a necessarily somewhat fore- 

 shortened position, with a W. long, of 16°, = -^ of the moon's 

 diameter, or as great, at least, as that of any lunar elevation. 

 Schr. is mistaken in ascribing this supposed height to the W. 

 end of the Prom. Archerusia, as it is evident, both from HeveFs 

 figure and description, that he refers it to the other end of the 

 promontory, in the immediate neighbourhood of Menelaus. 

 The assertion is not borne out, and seems not to have been 

 thought worthy of remark, by later selenographers ; yet Hevel 

 was so careful in his way that it might be as well to examine 

 whether any shaded depression, where the terminator crosses 

 the M. Serenitatis, may cause an illusory effect of projection. 



B. and M. here call attention to a very curious fact, that all 

 the mountain ridges proceeding from Menelaus run in a S.W. 

 direction, and that this parallelism extends not only through 

 all these high lands, but prevails also almost exclusively 

 through the greater part of the Apennines (23), and all the 

 mountainous regions lying to the S., as far as the craters 

 Pallas and Bode (28), and to the other side of the equator, 

 flattening even the circular forms of the craters in its way. 

 They further observe that since what we call W. on the moon 

 [i.e. turned to our W.) would appear E. to an eye trans- 

 ported there (an apparent reversal of bearing taking place in 

 looking at the moon, just as when we stand face to face with 

 another person, whose right hand is opposite our left), there- 

 fore this S.W. direction of lunar parallelism corresponds 

 in reality with that from S.E. to JST.W. so prevalent on the 

 terrestrial globe. 



Menelaus is the starting point of several luminous streaks, 

 which for the most part belong to the M. Serenitatis, except 

 one which runs to the S.E. Occasionally, B. and M. say, 

 this streak, a strong one in the M. Serenitatis, and some 

 others lying N. and S. in the same direction, appear to be only 

 portions of one great ray reaching from Tyeho to Thales, 

 through upwards of 1800 miles. This is more evident with 

 low powers, which, however, are apt to give apparent unity 

 where higher ones show distinction. 



