12 REPORT—1868. 
“Celestial Objects’, with two catalogues of the principal craters, &c., together form 
an excellent guide to observers who are commencing the study of “ detail.” 
It is by means of the study of “detail” that a definitive answer must be given 
to either of the questions mentioned at the commencement of this paper. The 
details of the moon’s surface are very various; mountain-chains, towering peaks, 
isolated hills, deep valleys, extensive plains scored with comparatively low ridges, 
crater-openings, in some localities crowded together by thousands, in others oc- 
cwring singly, and situated far apart from each other, rings (apparently the highest 
parts of crater-walls) the interiors of which convey the idea of having been partially 
filled with an injected material, minute craters are not unfrequent on their sur- 
faces ; bright spots, often of a dazzling whiteness, marking the tops of mountains 
and the crests of mountain-chains, as well as others of less brilliancy and greater 
indistinctness of outline ; dark spots surrounded in some cases by bright rims; in 
others the difference between the dark spots and the comparatively lighter surface 
is rendered distinctly visible by a sharp outline inclosing the dark surface. AI 
these varieties must be carefully studied before a conclusion can be drawn as to the 
unalterable stability or mutation of such objects. 
The means which we possess for the study of lunar objects may be considered as 
twofold,—the examination of delineations and topographical notices on the one 
hand, and personal observation of the objects themselves on the other, of course 
including a comparison of one with the other. For example, we may find on the 
moon a spot darker than any object in the immediate locality surrounded by a rim 
brighter than the exterior surface, and we record its appearance. It is now desirable 
to place in juxtaposition all the records we possess of it as under. 
Beer and Midler, in ‘ Der Mond,’ p. 304, thus describe two craters on the 
Mare Nubium. 1 am indebted to W. I. Lynn, Esq., of the Royal Observatory, 
Greenwich, for the translation. 
“The boundary of the Mare Nubiwm does not run alongside of Alpetragius, but 
passes by it under several deep curvatures from three to five miles [German] to the 
eastward. In the Mare itself is situated the bright radiating crater B (9° light) 
at —14° 55’ lat. and —7° 27' long., and near this the far larger and deeper one a, 
which, however, is found with difficulty at the full moon. It is about 43°, and the 
interior 8° bright (Insula Lesbos H).” 
As it is important that nothing should be quoted from memory unless quite un- 
avoidable, the following are extracts from my note-book. 
1868. June 29, 8.40. Crossley Equatorial, 7-3 inches aperture, power 122. 
“ B. & M’saand B are both quite conspicuous; a is a shallow crater or ring 
with a smooth floor; interior west shadow very narrow between 0:1 and 0-2, the 
diameter of a being 1:0. B isa deep and bright crater, shadow gibbous =0°5.” 
1868. July 29, 10.30, Royal Astronomical Society’s Sheepshanks telescope 
No. 5, aperture 2°75 inches, power 100. 
“ The interior of a very dark, the darkest surface in the locality, probably +2°.” 
1868. July 31, 10.15, R. A. 8S. Sheepshanks No. 5, power 109. 
“The floor of a is darker than any surrounding part; all three authorities, Lohr- 
mann, Midler, and Schmidt, make it lighter than the surface of the Mare.” 
The following brightnesses were determined :— 
a July 31, 10.15 to 10.50. August 1, 11.45. 
Alpetragius 
. B=08 0:8 
Mare Nubium =0:2 0-2 
Alpetragius a=0:175 0-15 
Billy =0:05 0:10 
Border Alpetragius a= 0-4 
Written from memory, Aug. 2 75. “ On the evening of the Ist, the line of de- 
marcation between the surface of the Mare Nubium and the adjacent lighter parts 
was very distinct.” 
With such facts before us can we decide for “change?” In replying to this 
question one disadvantage immediately suggests itself. We are uncertain as to 
the number of observations on which the earlier records rest ; but while in doubt 
