OBSERVATIONS OF LUNAR OBJECTS. 297 



1870, November 14. — Mr. Pratt at 10 hours recorded as follows : — 

 " Definition very bad ; a large area of the floor to the S.E. shaded off deli- 

 cately, as of a slightly lower level. Tint of unshaded part a little darker 

 than the surrounding Mare, that of the shaded portion as dark again. The out- 

 line of the shaded part conforms roughly with that area of the floor adjoining 

 the inner edges of streaks b and k." [Mr. Pratt has furnished a sketch, dated 

 1870, November 15, 11.50, which I apprehend from his letter, combined with 

 the date of his observation, should be November 14, and that the S.E. part 

 of the floor should be S.W. ; with these corrections the sketch and observa- 

 tions, agree.] Mr. Pratt's record proceeds thus: — "These observations have 

 much confirmed in my own mind some previous ideas, faintly shaped by 

 former views, that the light-streaks are merely parts of the floor relatively 

 raised and perhaps more rugged and broken (hence one cause for their con- 

 trast in tint with the rest of the floor), and that the spots are, especially several 

 of them, raised : perhaps they are the centre points of the latest activity, which 

 also possibly produced the streaks by raising them above the level. Was it 

 by successive deposits of ejected material ? One would have expected a lava- 

 like deposit after reading Piazzi Smyth's ' Tenerifl'e.' " [The contrast of colour 

 is a most important study, which may be greatly advanced by continuous 

 observations of the variations in intensity of two or more neighbouring spots.] 

 On the same evening, November 14, Mr. Gledhill recorded the floor as light, 

 =0-33, and the streaks as very faint. Mr. Gledhill noticed that the floor 

 was separated into a lighter and darker portion, the line of separation con- 

 sisting of the west edge of the sector produced to meet the north border. The 

 floor to the east of this line is bright, and to the west darker. [This line 

 would be nearly in the direction of the fault in the neighbourhood of which 

 the surface is raised, and the difference of tint is most likely produced by the 

 obliquity of the sun's rays.] Mr. Pratt's sketch is in perfect accordance with 

 Mr. Gledhill's observations. 



1869, October 26.— Mr. Gledhill recorded the floor as bright, =0-33. The 

 spots, except No. 1, were not readily seen ; the sector and streaks were faint. 



Summari/.— Sun's altitude 11° 38'-2 to 7° 48'-l ; tint of floor 0-39 to 

 0-36. 



Interval 24 to 12 hours. 



1869, September 27. — Mr. Gledhill recorded the floor as not so dark as the 

 Sinus Iridum, nor so light as that of Archimedes; itis registered as light, =0-33. 

 Mr. Gledhill described the streak c as a broad band of brightness, width 

 about one third the distance from the north rim to spot No. 1, enclosing 

 spots Nos. 13, 19, and 16 ; the streak /3 he described as a faint belt from 

 spot No. 3 to the east edge of Plato. The limits of both bauds were very 

 indefinite. 



Summary.— Sna's altitude 7° 48'-l to 3° 54'-8 ; tint of floor 0-36 to 0-33. 



Interval 12 to hours. 



1869, October 27. — Mr. GledhUl recorded the sector as very faint and 

 indefinite ; the streaks all very faint indeed, yet all seen at best moments. 

 Floor registered as light, =0-33. 



1870, November 15. — Mr. Gledhill recorded the floor as light,=0-33, but 

 consisting of two parts, the eastern light and the western dark. Mr. Pratt's 

 observations, 1869, August 28, interval 36 to 24 hom-s, were similar in cha- 

 racter. See Report Brit. Assoc. 1871, p. 86. 



Summary.— Sun'B altitude 3° 54'-8 to 0° 0' ; tint of floor 0-33 to 0-30. 



