OBSERVATIONS OF LUNAR OBJECTS. 75 



two places an extremely distinct unveiling or brightening which closely re- 

 semhled a very faint tivilight. Both places appeared dark, blackish, and con-' 

 trasted so slightly with the other night-shadows, that at first I was uncertain 

 whether or not I perceived a real difference in the obscurity. Meanwhile, 

 after a few seconds both the liglit-spots became somewhat brighter, changed 

 their form continually, until they soon became larger and notably brighter, 

 and assumed the appearance given in fig. 8 ; and as no very marked change 

 occurred while the obsei'vation was being made, I was by this time able to 

 sketch them in their present clearer colour and increased size ; but even yet 

 they appeared a dark grey, so that, according to my arbitrary scale and a 

 very approximate estimation, they were placed at only ^°, or at most |°. 



" Doubtless these present but always very dark colours were half-shadows, 

 and were found there because in these two places only a part of the rising- 

 sun was visible over the irregular elevations on the western border; and 

 these half-shadows I have often seen in the course of my observations when 

 the terminator passes across grey surfaces. Soon after, the surface threw off 

 the mask of night, and in a few minutes I could distinguish the line-like 

 shadows lying across the whole floor thrown by the peaks on the western 

 wall. If one, however, compares the shape of these two somewhat bright 

 spots on the map with the position and shadows of the west border, and re- 

 flects that these bright spots, as I saw them, were surrounded by the shadows 

 of night on the east, there can no longer be any doubt (if a different reflec- 

 tion of the light has no share in the matter) that the floor is not perfectly 

 flat, but that these two places are somewhat more elevated ; and with this 

 sujjposition the observations given before quite agree." 



The following notes have been kindly furnished by Mr. Pratt, relative to 

 the foregoing description of sunrise : — 



" Jan. 10, 3^. On 1870, March 10, 1 have notes of the same phenomenon, 

 which I believe I forwarded at the time, recording the inability I experienced 

 to rid myself of the idea that I was witnessing a true twilir/ht. My observa- 

 tion of it extended over twenty-five minutes, at the end of which time I 

 perceived the faintest trace of the formation of the spires." 



"Jan. 10, 4"^ 18"*, spot No. 3. Query. Is the brightest spot of the streak, 

 here mentioned as seen inclined to the north of No. 3, and I presume in close 

 proximity to it, my spot No. 30 ? As far as I can understand the localities 

 are identical." 



" Jan. 10, 4'' 50™, shadow of peak y. On a similar occasion I have ob- 

 served the thin thread of the shadow lying across II EV'S, and have watched 

 it slowly shortening and travelling down the interior slope of the rim, and had 

 a good view of it lying on the floor just in contact with the foot of the slope." 



" Jan. 10, 8*", shadow of peak h. I do not remember to have ever seen 

 the shadow of d otherwise than with the northern fork the longest." 



On Bianchini's light-streak Mr. Pratt remarks : — " Bianchini's ruddy spire 

 of light, which he observed at Rome, 1725, Aug. 16, and thought to be sun- 

 light shining through an aperture in the west wall, would the want of 

 achromaticity in his 150-palm telescope account for the colour ? Still his 

 unique view may prove valuable some day ; and it is stimulating to perse- 

 verance on our part to multiply observations with our comparativelj^ luxu- 

 rious instruments to find such unwieldy telescopes capable of so much in the 

 hands of a careful observer. I wonder if the crater G on the west exterior 

 slope was recorded so long since, as its clean-ciit form, as I have sometimes 

 seen it, is suggestive of recent formation, and its localitj' such as to easily 

 account for the fiUing-up of the aperture Bianchini supposed." 



