198 The Moon. 



affected by libration ; its measure from E. to W. varying at 

 different times from 06 to 0*8 of that from N. to S. Its 

 general appearance is that of an irregular oval extended along 

 the lunar meridian, and we should not have supposed, from 

 mere inspection, that in consequence of the perspective fore- 

 shortening it is actually elliptical the opposite way, its longer 

 axis pointing towards the eye, or more correctly from W.S.W. 

 to E.S.E. of the lunar compass. In this direction it extends 

 nearly 354 English miles ; from N. to S. about 280 miles, or 

 about the distance from London to Newcastle. Its area is 

 about 78,000 square miles,* frith part of the visible hemis- 

 phere of the moon, ten times the surface of Yorkshire and 

 Lancashire united, or a little more than half as much again as 

 the area of England and Wales, though of a very dissimilar 

 form. Of this, however, only 5-ths can be considered level. 

 Its border is not everywhere continuous, being interrupted in 

 some places, especially towards the W., on which side narrow 

 arms or straits penetrate the mountains, and communicate with 

 smaller grey surfaces. No " sea" is equally dark in compari- 

 son with its mountain boundaries, having generally only 2° to 

 2\° of light, grey in tone, mingled with dark green ; but the 

 latter colour, according to B. and M., for I have never seen it, 

 is perceptible only a few days before and after the full moon, 

 with a large ajjerture, a moderate power, and very favourable 

 weather, and, except near the Promontorium A g arum, nowhere 

 extends to the W. limit. It has been represented by Professor 

 C. Piazzi Smyth, in his three general views of th*s surface, 

 sketched with the feeling and spirit of a genuine artist, but 

 entering little into detail. " Practice and experience," he 

 says, "brought to view so many decided and -interesting 

 features of colour," that the idea of employing black and white 

 alone had to be abandoned. The surrounding region ranks as 

 5° of light, in some spots rising to 0° and 7°. Mountains en- 

 compass it all round, attaining a considerable height on the 

 NE. side ; here, in a line passing through Ficard A and B, 

 B. and M. have measured a summit of 13,300 feet, and further 

 to the 8.S.B. others of 7,150, 11,300, and 0,700 feet; these 

 decline at OHCe precipit* msly to the plain, from which they 

 must exhibit ;i magnificent spectacle, and over which they must 

 command a marvellous prospect. Such views are of frequent 

 occurrence in the moon, and the rapid rounding-offof so eom- 



* Something appears to have gono wrong hero in tho text of B. and M., as, 

 assuming their length and breadth to be correet, tho area they have given is con- 

 siderably too small. I have corrected this ; but am sorry to add that something 

 has gone mnch more wrong in this place in my little book, entitled Celestial 

 Objects for Common Telescopes, where, from using an erroneous multiplier, I have 

 made the area only 14,200 square miles ! I find, however, a similar mistake in 

 Cosmos, iv. 4'J2 (Bohn). 



