52 The Lunar Arctic Region. 



upon it a faint illumination reflected from their own crests, on 

 which the sun never ceases to shine. From this region the 

 centre of the earth is never seen higher than 7°, and the sun 

 rises only to 1^° above the lunar horizon. 



Mare Frigoris (W. half). — This on our map is the portion 

 of the shading lettered B, extending from the first meridian 

 (which of course stretches between the letters N and S) towards 

 the "W. as far as Nos. 4 and 5. (It should be observed, by the 

 way, that the shading on the map is not intended to represent 

 the precise form of the plain, which is very indefinitely bounded, 

 but merely to indicate its general position.) It is a grey level 

 of a feeble yellowish or greenish-yellow grey, and looks often 

 exactly like a strip of cloud lying across the moon. It contains 

 nothing very remarkable. The Lacus Mortis is a continuation 

 of it between Nos. 5 and 17. This flat incloses towards its 

 middle a tolerably conspicuous and deep crater named Burg, 

 with a central mountain. Its depth as measured is about 

 6800 feet. 



The Lacus Somniorum (C in our map) continues this level 

 landscape, but with many irregularities, as far to the S. as the 

 border of the Mare Serenitatis (E), from which it differs by 

 being much less flat and even, as is evident when they are both 

 intersected by the terminator at the same time. " If the sup- 

 position," say B. and M., " of a watery covering on the moon 

 were admissible, the Mare Serenitatis might have been com- 

 pared to a deep sea, diversified by islands and insular chains ; 

 the Lacus Somniorum, on the contrary, to a shallow expanse 

 of water, which allows the irregularities of the bottom to ap- 

 pear through it." 



Our guides now carry us across to the range of mountains 

 called Taurus (the centre of which is marked 8 on our map). 

 This is an extensive region, bounded by the Mare Serenitatis 

 on the E., the Lacus Somniorum on the N.E., the Mare 

 Tranquillitatis (D) and its subdivision the Palus Somnii on the 

 S., and on the W. by the range of large craters extending 

 northwards from the Mare Crisium. It readily divides into 

 one great mass to the N. and two inferior groups to the S. 

 and S.W. — the first containing the craters Romer and Posidonius 

 (9, 10); the second a crater called Vitruvius ; the third, the 

 craters Macrobius (11) and Proclus (12). The mountains are 

 for the most part arranged in labyrinthine masses, intermingled 

 with plains and valleys. 



Romer (9) is a ring-mountain with a very broad and ter- 

 raced wall. Its depth is computed to be 11,500 feet (Schroter 

 gave 8600), with a breadth of about 25 miles ; and its interior 

 contains a mountain (5000 feet high according to Schroter), 

 and a bright crater. To the N. of Romer, Lohrmann, upon 



