OBSERVATIONS OF LUNAR OBJECTS. 291 



fined ; as usual, of all the streaks a is always brightest ; /3 is one of the 

 brightest, but less so than a ; y is similar ; jj is bright and mostly well seen ; 

 (, €, d, and ^ are always the faintest and broadest ; e and ( are almost always 

 seen, S not always ; that portion of a which lies to the west of spot No. 16 is 

 not always seen " [this answers either to " o " or e]. Mr. Gledhill described 

 and figured a short streak from the N.W. border very bright. On this I 

 remark : — " The elbow of light tint described by the Kev. T. W. Webb as seen 

 by him on Oct. 24, 1855 (see monogram of the Mare Serenitatis, p. 13), was 

 well seen (and very bright) by Mr. Gledhill, 18(39, Nov. 19, moon's latitude 

 4° 10' + S. On the 16th the moon's latitude, 5°, was more favourable for 

 seeing it ; but it does not api)ear, from Mr. Gledhill's observations, that it 

 was then visible." See Mr. Gledhill's remarks on the streaks y, /3, and rj, 

 ante, p. 283. 



It woald appear that, so far as the streaks are concerned, the N.W. part of 

 the floor exhibits the greatest amount of variation. Looking at Mr. Gled- 

 hill's diagram of November 19, and taking into consideration the general 

 structure of the floor, we have in the S.W. the arms of the trident radiating 

 from spot No. 1; in the S.E., the sector fan-shaped, the sides radiating from 

 spot No. 4; in the N.E., /3 specified by Mr. GledhiU as one of the brightest 

 streaks from spot No. 3, and a, (i, t], and y more or less parallel. Now 

 bearing in mind that Plato has suffered dislocation from a fault from N.W. 

 to S.E., that spot No. 1 is opened upon the highest part of the floor, and that 

 spots Nos. 3 and 4 occur on the N.E. slope from the fault, it is not a little 

 significant that the directions of the streaks are from higher to lower ground. 

 Mr. Pratt suggests that the light-streaks are coincident with formations 

 analogous to " spurs " from the chief centres of the residual activity on the 

 floor (see Report Brit. Assoc. 1871, p. 95). 



1869, November 19. — On this evening Mr. Gledhill observed the streak a 

 and its continuation " o " ; he also saw, forking from the locality of spot 

 No. 16, the curved streak c, convex to the west border (see ante, pp. 263, 

 264, 285, 289). On contrasting Mr. Elger's and Mr. GledhiU's sketches of 

 Sept. 20 and 25 respectively with Mr. Gledhill's of Nov. 15 and 16, and espe- 

 cially of Nov. 19, the existence of c and " o" as separate streaks is imdeniable. 

 On Sept. 20 and 25 " o " was distinctly recorded by two independent observers ; 

 it was also recorded on Oct. 25, 26, and 27 by Mr. Gledhill. On Nov. 15 it 

 was not seen by Mr. Gledhill, nor on the 16th, the streak c passing over and 

 beyond spot No. 13. On Nov. 19 there was a great development of light- 

 streaks, the N.W. part of the floor exhibiting the curved streak c, with " o " 

 and a and Webb's elbow in contact with the N.W. border. Mr. Pratt recorded 

 the N.W. streak making a contact with the N.W. border, near spot No. 16, 

 on Nov. 15. 



1870, October 10. — Mr. Elger recorded y and /3 as plain, jj faint; the con- 

 nexion by p between the centre (e) and eastern (i^) arms of trident seen. 

 Trident and markings on N.W. side of floor as on the 9th of October. Spot 

 No. 5 is recorded as seen on the east edge of the east arm of trident (see 

 ante, pp. 254 and 275). Messrs. Pratt and Neison recorded the floor as 

 " medium," and Mr. Gledhill recorded it as " very dark." The lighter tint, 

 as seen by Messrs. Pratt and Neison, is exceptional. Mr. GledhUl mentioned 

 that the sector was composed of bright lines radiating from the apex to the 

 base (see ante, p. 285). Mr. Elger witnessed a similar appearance on April 14, 

 1870. (Interval 132 to 144 hours.) 



Summary. —Sun's altitude 39° 50'-5 to 39° 9'-2 ; tint of floor 0-66 to 0-65. 

 Streaks generally visible — the sector, east and middle arms of trident, with 



x2 



