28 Lunar Details. 



LUNAR DETAILS. 



BY THE EEV. T. W. WEBB, A.M., F.E.A.S. 



In our last paper we did not quite terminate the subject of 

 Proclus (12). This crater is the origin of several luminous 

 streaks, which, however, are well seen only under favourable 

 circumstances. Two take the direction of the Mare Grisium, 

 and may be traced as far as its centre. Schroter, on one occa- 

 sion, 24h. after Full, when the W. edge of the plain lay on the 

 terminator, perceived three crossing nearly its whole extent. 

 This grey level should be watched with reference to variations 

 of this kind. From more than one source I have been favoured 

 with observations proving that something similar to the ap- 

 pearances described, in Int. Obs., v. 203, may occasionally be 

 perceived.* A collection of radiating streaks also issues from 

 Proclus towards the N.E. In this direction a very sharp and 

 nearly straight line connects Proclus with a small crater, Pro- 

 clus d. This line marks the course of a slight declivity, at the 

 foot of which lies the — 



Palus Somnii, a remarkably well-bounded and always dis- 

 tinguishable region, E. of Proclus, having a form somewhat 

 resembling an irregular rhombus, or heraldic "lozenge." B. 

 and M. observe that its colour is quite peculiar, but difficult 

 to be designated ; something of a yellowish brown. It is alto- 

 gether occupied by hills of no great elevation, chiefly following 

 a meridian direction ; and its aspect is singular, unlike that of 

 the other regions which Riccioli comprises under the general 

 term Paludes, but probably much resembling many regions of 

 our own globe. The region S. of Proclus is of a somewhat 

 similar character : the shortness of the shadows here thrown 

 towards the Mare Tranquillitatis (D) and the M. FoecunditaUs 

 (P), as compared with those falling in the direction of the M. 

 Grisium (A), indicate the considerably deeper level of the latter 

 surface. 



The Mare Tranquillitatis (D) gives rise to a remark by B. 

 and M., that from a merely superficial glance at the lunar disc, 

 it might appear as though its seas were diverse only in form 

 and magnitude ; but a more careful comparison under various 

 incidences of light will bring out so many peculiarities in each 

 of them, as alone to prove, even if no other grounds for the con- 

 trary belief existed, the insufficiency of the assumption of a gene- 

 ral covering with water or any other homogeneous fluid. This 

 extensive plain is divided from the M. Serenitatis on the N.E. 

 in a singular way, by a very straight and continuous slope of 



* See Mr. Slack's observation, Int. Ob3. yii. 322. 



