OBSERVATIONS OF LUNAR OBJECTS. 277 



clearly up to the border, but it is very bright close to the border. " It 

 seems," says Mr. Gledhill, " as if it were thrown off by the bright lofty wall 

 close to the north of HE'/' 2." [The dip of the floor to the border all round 

 has been well determined. Does not this dip prevent not only the tracing 

 of the streak, but its really extending as far as the border?] The sector 

 passes on to spot No. 3, d (?) meets e about halfway from the west border to spot 

 No. 1 (see ante, p. 247, fig. 1); they are both well seen, are sharp, and the 

 dark space between them is sharply defined. On the same day Mr. Elger's re- 

 cord was as follows : — " The sector could be traced from spot No. 4, through 

 No. 17, to the southern rim, and from No. 4 to the south of the triangular 

 formation, II E '/' 2, on the eastern rim ; but it was very faint and badly de- 

 fined. The streak y was not seen ; but I remarked that the N.W. portion of 

 the floor, especially near the border, was much lighter than the remainder. 

 No traces of the trident." 



The difference between the observations of Mr. Gledhill and Mr. Elger is 

 mainly attributable to difference of aperture, with a probable difference of 

 atmosphere ; they both agree in the greater luminosity of the N.W. part of 

 the floor in the neighbourhood of Webb's elbow. 



1869, August 16.— See a7ite, p. 251. 



1870, December 2. — Mr. Elger described the sector as very faint. 



1870, November 2. — Mr. Elger recorded " faint traces of the sector." Mr. 

 Neison remarked that the streak of light near spot 17 (the sector), was much 

 darker, or rather less bright than usual. 



Sumnmry. —Bnn'B altitude 11° 38'-2 to 15° 23'-3 ; tint of floor 0-39, esti- 

 mated from curve. Streaks generally visible — sector, arms of trident, and 

 those on the northern and eastern floor, viz. Webb's elbow, c, a, fi, t], and y. 



This interval has been characterized by an extension of the sector as far 

 as spot No. 3 on January 11, 1870, and of streak fj beyond the same spot 3 

 on the same day. Were these extensions due to activity in group 3 ? It 

 may be noted that streak a was well seen on the same day. Another inter- 

 esting feature of the interval is, the retention, during the night between 

 sunset in March and sunrise in April, of the quality by certain portions of 

 the floor by which they reflect light more strongly than under ordinary cir- 

 cumstances. The extreme faintness of the sector on November 2 and De- 

 cember 2, 1870, as weU as its general faintness, is remarkable. 



Interval 48 to 60 hours. 



1871, March 1. — Mr. GledhiU recorded the floor as Light, =0-33; streaks 

 very faint, not well seen. Mr. Elger described them as generally faint, espe- 

 cially those on the southern part of the floor. 



1870, May 10.— Mr. Elger speaks of the sector and streak y as very bright 

 and sharply defined, /3 much brighter than n. Trident faint, especially the 

 west arm e. The lighter portion of the floor near the N.W. border was faint, 

 especially at the west ; it appeared to follow the curvature of the border of 

 Plato. No trace of the elbow. Mr. Gledhill recorded the floor as " near 

 medium" [registered =0-50], and the streaks brighter than last night [the 

 9th]. Mr. Gledhill mentioned his ha\'ing seen a, from which it may be in- 

 ferred either that the streak was really brighter than on the 9th (see ante, 

 p. 273), or that the brightness on the northern part of the floor had declined 

 in intensity. Mr. Pratt says : " b [the sector] and k were of the streaks the 

 most visible. The whole of the western end of the floor which was in hght 

 appeared covered by a continuous haze of brightness, the chord of the arc 

 running nearly N. and S. ; a faint glimmer of i^ was all that was possible." 



