50 The Lunar Arctic Region. 



made sufficiently prominent in their map. Its long-enduring 

 shadow, however, under a favourable libration, proves it to be 

 a very important object, and one of the leading features of the 

 district, and it would be desirable that it should receive a suit- 

 able designation in the enlarged nomenclature which Mr. Birt 

 is engaged in carrying out. This portion of the Moon does not 

 bespeak any especial care on the part of B. and M. It should 

 have been noticed in our last paper that, though they have 

 drawn, they have not described two curious streaks S. of Her- 

 cules, which distinctly converge upon the little bright crater in 

 its interior, though they are lost before they reach the external 

 foot of the great wall. Between Qeminus also and Thales is a 

 curious arrangement of light and shade, neither drawn nor men- 

 tioned by them. As to drawing there is little to be said. It 

 was a hopeless undertaking to combine in one representation 

 the local colouring of the lunar noon with the true relief de- 

 veloped by the shades of morning or evening. A separate pic- 

 ture is wanted for the Full Moon, a chart or diagram for the 

 phases. It would, however, have been more satisfactory to have 

 found some account of a fine broad streak, somewhat like the 

 tail of a comet, which I have seen 3d. 15h. after First Quarter, 

 5d. 22h. after greatest S.W. Libration, passing from the region 

 of Geminus just S. of Struve, and forming the S. shore of the Mare 

 Humboldtianum, of which it seems to flatten the curve. Between 

 this place and Endymip?i it is subdivided into two or three nar- 

 row rays, and between Mercurius (a considerable crater N". of 

 Struve) and the M. Humboltltiavium, it is crossed by another re- 

 markably thin, straight, and even streak ; the intersection of the 

 two forming a patch of light more brilliant than either of them 

 separately. This is a suggestive circumstance and worthy of 

 attention. The last-mentioned streak is of considerable length ; 

 its actual bearing upon the Moon is probably S.S.E., and not far 

 from perpendicular to the other, though foreshortened into great 

 obliquity of position : it becomes gradually invisible either 

 way ; in one direction between Struve and the limb ; in the 

 other, beyond Endymion, where if it is not lost, it bends more 

 to the S., or perhaps another ray takes up its course and runs 

 into Thales. All this, of which no note is to be found in B, 

 and M., is merely a specimen of what is to be met with in many 

 regions in the high illumination of the Moon. 



At some distance E. from Thales we come upon a district 

 remarkable for a network of intersecting ridges, by which it is 

 mapped out into separate areas, of various, occasionally even 

 rectangular forms. There seems little difference of level or 

 colour: the ring-mountains which occur are flat: craters, some 

 of them of great brilliancy, have broken alike through the 

 ridges and the plains. Still further N., B. and M. have spoken 



