ga REPORT — 1871. 



in different parts of the floor, even in so contracted an area, the whole 

 northern half being less well defined, the south-east part the best so by 

 far. Traces of the line from m to Eambleta were caught, and the floor 

 appeared unlevel, the central and south parts appearing highest, and the 

 south-west part next so. This, Mr. Pratt says, requires confirmation. 



1870, September 14. Mr. GledhiU records No. 3 as a fine wide double spot 

 (i.e. 3 and 30). Mr. Ncison (same day) remarks as follows of Nos. 1, 

 3, and 17, seen by Mr. Gledhill as craters : No. 1 not very distinct ; No. 3 

 sharp and shaded, not very bright ; No. 17 very distinct. 



Interval 72 to 60 hours. 



1870, August 16. Mr. Pratt observed 3 spots only this evening. On 

 October 14 (same interval) 16 were observed, 9 by Mr. Gledhill and 7 by 

 Mr. Pratt, in addition. They both record the definition of the border as 

 "good;" Mr. Pratt says, "with interruptions." On August 16, Mr. Pratt 

 records the definition of the border as "bad." The following remark of Mr. 

 Pratt is interesting in connexion with this paucity of spots : — " The darker 

 parts or shaded portions of the floor were just perceptible with attention. 

 ' Tint of floor' medium, much paler than on the 13th inst." 



Interval 48 to 36 hours. 



1870, August 17. Mr. Gledhill records No. 1 as a fine, large, open crater, 

 3 and 30 as craters, 17 as a small crater, and 4 as a bright but not de- 

 finite spot. 



Interval 36 to 24 hours. 



1870, March 23. Mr. Gledhill writes : " The shadow of the elevated ob- 

 ject on the east border (the rock !!,), close to the N. of "W. II YJ''^, was on 

 the floor, and the adjacent floor to the N.W. was very bright, much brighter 

 than a or the ' sector,' and it extended one third of the distance from the 

 border to spot No. 4, as in sketch." Mr. Gledhill could not determine its 

 form, but considered that it was the streak tj intensified. 



1870, July 19. Mr. Gledhill observed the four craters 1, 17, 3, 30 only; 

 he described No. 1 as a large circular crater with raised walls, but not 

 much brighter than the floor. 



1869, August 28. Mr. Pratt writes : " The level of the floor was con- 

 spicuously divided by the line from m to c, the ground sloping east and 

 'west of this lino, the eastern part being brighter than the part on its west, 

 while the locality of spot No. 4 was judged to be the highest of the whole 

 floor." In connexion with this remark of Mr. Pratt it may be well to 

 "notice that, combined with Mr. Elger's observations on 1870, Jan. 10, of 

 ■a depression in the floor east of No. 1 (see Interval 12 to 24 hours), the two 

 suggest that this depression does not extend so far as No. 4. Again, com- 

 paring this observation of the western part of the floor being darker than 

 the eastern, which is in accordance with Mr. GledhiU's on March 24, 1870 

 (see Interval 12 to hours), it would appear that Mr. Elger's observa- 

 tion of the bright western area on 1870, May 9 and 10 and August 6, was 

 an intensified brightness of the ordinary brilliancy of the floor, sloping to the 

 west. The Intervals 24 to 36 and 48 to 60 hours, the season spring, with 

 the sun's altitude about 14°, seem to indicate that the increased brightness 

 was quite independent of illuminating angle. 



Speaking of the ajiparent changes observed, not only on Plato, but over 

 a -wider range, between August 16 and 28, 1869, Mr. Pratt says : " Thus, 

 among apparent changes of a particular characterj and restricted to certain 



