Neighbourhood of the Lunar Spot, Mare Grisium. 359 



NEIGHBOURHOOD OF THE LUNAR SPOT, MARE 



CUISIUM. JUPITER'S SATELLITES. 



OCCULTATIONS. 



BY THE KEV. T. W. WEBB, M.A., F.R.A.S. 



Oue somewhat lengthened examination of the interior of the 

 Mare Grisium did not admit of our extending our survey beyond 

 its immediate boundaries. Its vicinity contains, however, some 

 interesting features. The surrounding elevated land is broken 

 up in many places by eruptive force, and some of the craters 

 deserve a passing notice. Gondorcet (see the diagram in our 

 April number) is a considerable crater, 45 miles in diameter, 

 with a very regular interior, but an exterior quite the reverse, 

 as is frequently the case where such formations occur in moun- 

 tainous regions. It is about 8900 feet in depth. Azout is a 

 similar but smaller crater, 16 miles in diameter; its interior 

 has only 2° of grey light. Four ridges of some height, and 

 nearly equal in length, run from its wall to the " sea/ ; includ- 

 ing between them three sloping bowl-shaped valleys.' Water- 

 courses, if they were possible upon the moon, might be looked 

 for in such localities, which are not of frequent occurrence. 

 This is the remark of Beer and Madler, to whom the reader 

 will understand that he is indebted, throughout these papers, 

 for all statements not expressly referred to other authorities. 

 I regret that in this, as in numberless other instances, I can 

 add no corresponding observation of my own ; and that with 

 regard to the greater part of the lunar surface I am unqualified 

 to act as guide, excepting upon the information of others. 

 Firmicus, more than 38 miles broad, and nearly 5000 feet 

 deep, is conuected with Azout by a mountain ridge. Like the 

 preceding craters it is of a uniform dark " steel grey," which, 

 under a high illumination, though of the same intensity of 

 light with the Mare Grisium, is different in colour, from the 

 intermixture in the latter case of green. Apollonius, 30 

 miles in diameter, is nearly S. of Firmicus, and is the furthest 

 in that direction of this crater group. The summit of its S.E. 

 wall is 5400 feet above the interior. 



To the W. of this object we come to a more level country, 

 remarkable under high lights for a set of broad, crooked, and 

 branching streaks of dark grey, somewhat resembling, ac- 

 cording to B. and M/s remark, the Saima lakes in Finland. 

 They seem under such circumstances to lie in a perfect plain. 

 Near the terminator, however, they aro perceived to be valleys 

 divided by banks of moderate height, and associated with 



