OBSERVATIONS OF LUNAR OBJECTS. 71 



Third. That spots I^os. 1, 3, 17, the object halfway between No. 4 and 

 the E. border (7), the object halfway + between No. 3 and the E. border 

 (32), the object (if any) just to the E. of No. 3 (31), and the object S.W. of 

 No. 1 at a considerable distance away are all elevated objects. 



[Some time subsequently to these observations I received from Mr. Gled- 

 hill a drawing of nine crater cones seen on Jan. 10, 1870. They were Nos. 

 1, 3, 30, 4, 7, 9, 11, 17, and 32. I have not received any conhrmation of 

 the object a considerable distance S.W. of No. 1.— W. E. B.] 



Fourth. The order in time of the apjiearance of the shadows. 



Fifth. The time to a minute when light first falls on the floor. 



[The discussion of the observations by intervals shows that the sun's light 

 first falls upon the floor of Plato from ten to thirteen hours after the sun has 

 risen at 4° &-1 of E. long, on the equator according to season ; a simple 

 computation of the epoch of sunrise at this longitude and © — S3 will be a 

 guide to ascertain the illumination of Plato within twenty-four hours of the 

 epoch.— W. E. B.] 



Sixth. The interval between the appearance of light on the floor and the 

 distinct perception of the shadows from the W. border is about twenty-five 

 or thirty minutes. 



Seventh. The great northern streak of sunlight is seen some fifteen minutes 

 before the southern streaks are detected. This may be caused either by dif- 

 ference in elevation of the gaps in the W. border, or diff'ercnce in level of the 

 floor, or both may unite to produce the effect. 



AVhat can cause the duskiness of the eastern floor except depression of the floor ? 



1870, Jan. 10, 9" 0°. Mr. Elger saw spot No. 1 close to the shadow of the 

 peak situated on the S. of the great gorge or opening in the W. wall. At 

 9'' 10"' the N. peak of this shadow was about clearing it ; at the same time 

 spot No. 4 could just be seen. Mr. Elger remarked that the shading round 

 spot No. 1 was much darker than the central portion of the floor, and that 

 this dark shading could be traced in an easterly direction to about one fourth 

 of the distance between the spots 1 and 4: " this," says Mr. Elger, " would 

 appear to indicate a fall in the surface of the floor from No. 1 towards 

 the E. in section" (fig. 5). Schroter, if I re- p- g 



member rightly, alludes to some observations indi- 

 cating similar irregularities in the floor. Erom 

 Mr. Elger's observation, combined with one of Mr. 

 Gledhm's to be noticed under Feb. 9, 1870, it would 



appear that spot No. 1 is situated on the ridge marking the great fault. (See 

 interval 24" to 36\) 



1870, May 8, 8" to lO*". Close of first interval of twelve hours. Epoch 

 7d 21" 20"", Mr. Elger writes, " On the evening of the 8th, between 8" and 

 10", I had a fine view of sunrise ; the air was remarkably steady ; shadows 

 and minute details seen to perfection." 



1870, May 18. Mr. Elger writes : — " Re your statement as to the dip of 

 the floor. Is there reliable evidence that the N.E. and S.E. areas of the 

 floor are lower near their respective borders than towards the spotless central 

 area ? In January last I saw spot No. 1 in contiguity with the shadow of 

 No. 2 peak (western wall) ; the surface of the floor east of No. 1 was then, 

 of course, seen under very oblique light. Judging from the shading and 

 general aspect of the surface in the neighbourhood of No. 1, there appeared 

 to be a veri/ rapid fall from spot No. 1 to spot No. 4 ; if this bo so, the 

 stem of the ' trident ' would be a depression in the surface." 



1870, April 9. Twenty-three hours after epoch of sunrise at 4° 4'-7 on 



