I 



OBSERVATIONS OF LUNAR OBJECTS. 293 



=3°-6 ; Plato, the W. part of floor, = l°-6 ; Grimaldi, S. part of floor, =0°-6. 

 These determinations exhibit increase of brightness with increase of num- 

 bers — Grimaldi the darkest, surface around Kepler the brighest. My estimate 

 of the tint of the floor of Plato, on the scale adopted for comparison with 

 the sun's altitude, was 0-66, or dark ; this is about a degree brighter than 

 the S. part of the floor of Grimaldi." 



1870, September 11. — The markings, as observed by Mr. Elger, were aU 

 indistinct. 



Summaiy.— Sun's, altitude 39° 9'-2 to 37° 57'-8 ; tint of floor 0-65 to 

 0'64. Streaks generally visible — the middle arm of trident, sector, and y 

 the most frequent ; the east arm of trident and the N.E. streaks less 

 frequent. 



Interval 144 to 132 hours. 



1870, April 17. — Mr. GledhiU recorded the floor as dark, =0-66, and the 

 N. streaks as brightest ; /3 as bright as the sector, and y, rj seen only at the 

 foot of the slope. 



] 869, May 27. — Mr. GledhiU records the sector as ill-defined below. 



1871, January 8. — Mr. GledhiU described the streaks as having been well 

 seen ; one, not named, as very sharply defined, bright, narrow, and straight. 

 This I apprehend to be a, as Mr. GledhiU generally describes it as such. 



1869, December 20.— Mr. GledhiU recorded the floor as dark, =0-66. 

 Streak seen (bright) ; sector a fine striking object. On the same evening 

 Mr. Pratt recorded the markings as peculiarly indistinct, from which he 

 considered the apparent difterence of form which he observed to arise. 

 The trident near spot No. 1 was shaded off. The greatest peculiarity shown 

 by Mr. Pratt in his diagram is a bifurcation in the neighbourhood of streak (3, 

 or rather two streaks from spot No. 3 instead of one. Mr. Elger on the 

 same evening showed one only, very narrow, and remarked the portion 

 of the floor between /3 and jj to be very dark. Mr. Elger further said, " a 

 remarkable feature observed was the strip of light (streak y), which during 

 the whole evening was by far the brightest marking on the floor." This 

 streak is not recorded by Mr. GledhUl, who noticed the sector as being the 

 most striking object. Mr. Elger saw a part of c and Webb's elbow i, which 

 he described as the brightest on this part of the floor. 



1870, August 13. — On this evening the floor was recorded as " dark " by 

 three observers, Mr. Pratt, Mr. GledhiU, and Mr. Neison. Mr. Pratt re- 

 marked: — " On this evening, as well as 1870, Aug. 12, the tint of the dark 

 portions of the floor was much intensified close to the rim ; it was the case 

 all round, but especially so between b and ^, between e and 4", and between 

 ft and J/." Mr. GledhiU observed the streaks to be very bright ; they appeared 

 to stand out in reUef. Compare with Mr. Pratt's suggestion (1870, October 

 17) of the light-streaks being analogous to spurs (Eeport, 1871, p. 95). 



1870, October 11. — Mr. Elger recorded the streak ij as very faint. 



Smnmary.— Sun's altitude 37° 57'-8 to 36° 17'-5 ; tint of floor 0-64 to 

 0'62. Streaks generally visible — the sector much more frequent than the 

 others ; next in order east arm of trident, y, ft, and a. The N.W. streak and 

 middle arm of trident less frequent, the others rarely seen. 



Interval 132 to 120 hours, 



1870, March 19. — Mr. GledhiU recorded the floor as dark, =0-66 ; he de- 

 scribed the sector and o as very bright, the brightest on the floor. 



1870, November 10. — Mr. Elger described the markings as better seen 



