OBSERVATIONS OF LUNAR OBJECTS. 265 



towards the south-west, the concavity waij in the o^jposite direction (see 

 Lunation November 1869, ante, p. 263). The streak a extended on the 14th 

 of April from Webb's elbow, and was quite separated from the northern 

 border of Plato. On the 15th it was recorded as very bright, the projecting 

 portion of c being brighter than on the 14th, and nearly joining the western 

 arm of the trident ; the continuation " o " was not seen. On the IGth c had 

 disappeared, n being recorded as bright and sharp. On the 17th it was re- 

 corded by Mr. Gledhill. 



In this lunation " o " -was seen from 36 to 84 hoiirs after sunrise. The 

 observations of April 11, 1870, and December 14, 1869, are synchronous as 

 regards interval from sunrise. On December 14 a and " o " formed together 

 the brightest and best-defined streak on the floor. On April 11 " o " was very 

 hazy and ill-defined. These opposite characters under the same solar alti- 

 tudes, as well as those recorded in the previous February lunation, cannot be 

 exijlained on the hypothesis of changes of illuminating angle, for there were 

 none, but point to some agency operating within the enclosure of Plato. 

 The appearance of the portion of c projecting towards the western arm 

 of the trident on the 14th, its nearly joining the arm on the 15th, and its 

 disappearance on the 16th, combined with the opposite directions of the 

 convexity in November and April, again point to recent or, we may say, 

 present local action. 



Lunation May 1870, from 24 liours after sunrise to 33 hours before 



meridian passage. 



The commencement of the observations during this lunation was charac- 

 terized by the north portion of the floor being brighter than hitherto observed. 

 On May 9 both Mr. Gledhill and Mr. Elger recorded independently this in- 

 creased brightness ; in consequence the streak a could not be traced. The 

 moon's latitude at midnight was 4° 21'-9 N., Plato at that time being north 

 of its mean position. On May 10 the streak a was seen by Mr. GiedhiU. 

 On May 12, interval 108 to 120 hours, or from 12 to 24 hours before the 

 apparition of the projection c in April, this marking, although plainly seen, 

 could not be traced so far to the south as in April, nor was it so sharply de- 

 fined as in that lunation ; indeed all the west portion of the north-west area 

 was hazy as on April 11 and 12, and also on June 10. While this haziness 

 characterized the western part of the floor, the area east of spot No. 16 was 

 free from it ; the streak «, as seen by Mr. Elger, was very bright and well 

 defined. Is not this indicative of the haziness being due to local lunar 

 action, and of the restriction of such action to a very small area of the sur- 

 face, also of the inefficiency of change in the illuminating angle to explain 

 it ? On May 13 the streak a was recorded as bright and well defined, and 

 very bright at the locality of spot No. 19. 



Lunation June 1870, from 105 to 69 Jiours before meridian passage. 



Two observations only were obtained during this lunation ; the first on 

 June 9, 72 to 84 hours after sunrise, when streak a (query its continuation 

 " ") had the same nebulous appearance which it exhibited on May 10 ; the 

 second on June 10, 96 to 108 hours after sunrise, when the eastern portion 

 n was bright and wcU defined, the western portion "o" hazy, partaking of 

 the general haziness of the north-west portion of the floor. These observa- 

 tions are in striking contrast with those of February (see ante, p. 264), in 

 which neither the haziness nor the continuation " o " were observed. The 



