The Moon. 205 



It is of a character "which we shall not unfrequently meet with 

 in our lunar travels, resembling a bowl nearly fall of a fluid 

 into which it is obliquely sinking ; in point of size and age it 

 seems more the counterpart than is represented in the diagram, 

 of the circle already mentioned on the other side of Picard d. 

 I first perceived it, 1863, Oct. 28, and have since repeatedly 

 seen it, under such varied incidence of light, that I cannot 

 doubt its reality, or understand how it is to be satisfactorily 

 reconciled with B. and M's. detail here. They have also 

 omitted two very minute craters, one a little way S.S.E. of e, where 

 they, Schroter, and myself at other times have seen an eleva- 

 tion ; the other between my ring and Picard d, lying apparently 

 on the serpentine ridge, in a part which was not visible when 

 the diagram was made, but is readily seen under the opposite 

 illumination. The pass or gateway through the E. mountains 

 is guarded, as I have several times noticed, by two small craters, 

 both seen by Schroter, but one only clearly represented by 

 B. and M. That on the N". side was not perceived by the 

 former observer till after he had had the spot under his eyes for 

 more than three years ; yet there is no reason to suppose it 

 new ; such oversights are not very uncommon. 



B. and M. have remarked it as a singular fact, that no central 

 hill is to be found in any of the craters in or around this great 

 plain, the nearest so characterized being Taruntius and Ma- 

 crobius (91 and 11 in the Index-Map), if we except a feeble 

 and somewhat uncertain trace in Azout. I have, however, 

 entered a low central hill, as visible in Picard, and another 

 more distinct in Picard A, with a 3 ^ -inch aperture, 1834, 

 Sept. 19 ; and with my present telescope I distinctly found, 

 1863, Oct. 28, that both these craters have interiors rough 

 with hillocks, especially A, which has an irregular mound lying 

 on the inner slope of its N. end; the effect being much as 

 though masses of soft mud had been thrown at random into 

 the interior. Gruithuisen states that near Picard some re- 

 markable white ridges are to be seen, in part as straight and 

 regular as artificial walls. 



In consequence of the great differences resulting from 

 libration, no certain age of the moon can be mentioned as the 

 most suitable for the study of this region. Opportunities must 

 be carefully watched in the young crescent and the early wane. 

 A grand effect is produced during the progress of the lunar 

 sunset, when the great boundary mountains on each side of 

 the E. gateway fling their ponderous shadows to the termina- 

 tor, inclosing a small portion of the plain, which still enjoys 

 the declining ray. This has been well figured by Schroter, 

 and I have seen it 3d. 4h. after the full moon. 



