292 REPORT— 1872. 



the northieru bifurcation of the western arm S, the N.W. and N.E. streaks 

 except 13, which is less frequent. 



Interval 156 to 144 hours, 



1870, July 14.— Mr. GledhiU recorded the floor as dark =,0-66. The 

 sector and streaks seen were dense and bright ; the streak rj was seen near 

 the border ; o had a condensed brightness in the middle ; the south ends of the 

 south streaks ^ and e were brightest. With powers 150 and 115 the sector 

 appeared to be condensed at the apex. On the same night (July 14) Mr. 

 IngaU speaks of the floor being, at times of fine definition, covered with spots 

 of Ught. I have registered it as very light, = 0-00 ; it must, however, be 

 considered as exceptional, the floor being dark under a high sun. This extra- 

 ordinary spottiness of the floor appears to be of the same nature as the ap- 

 pearances of the Mare Crisium, related in Webb's ' Celestial Objects,' third edit., 

 pp. 82 & 83. Mr. lugall gives the distribution of the markings as follows : — 

 First. A. large white cloud stretching half round the crater-floor from spot 

 No. 14 to spot No. 3. This white cloud occupies the position of the middle 

 and the^east arms of the trident and that of the sector, with its extension to 

 spot No. 3, the sector and the two arms of the trident being connected. It 

 is remarkable that this cloud is entirely separated from the border ; and, so 

 far as the sector is concerned, we have a similar observation by Mr. Elger on 

 May 13, 1870. (See Interval 132 to 144, ante, p. 286.) Seco7id. A detached 

 fainter cloud on the N.W. part of the floor, which occupies precisely the posi- 

 tion of the curved streak c, with its convexity towards the border ; it incloses 

 spot No. 16. Third. A small detached mist on the S.W. part of the floor, 

 which occupies the position of GledhiU's streak 6. Fourth. A curious brush 

 of light adjoining the N.W. border (Webb's elbow), much brighter near the 

 wall. The difference between Mr. GledhiU's and Mr. IngaU's observations, 

 particularly as regards the absence of streaks near the border, except Webb's 

 elbow, which characterizes Mr. IngaU's, is doubtless due to the difference of 

 apertures. The elbow appears to have been seen well in both instruments. 



1869, August 23.— See atite, p. 253. 



1870, November 9. — Mr. Elger recorded the markings as faint, except the 

 sector and y ; the latter is described as unusually bright. 



1869, October 21. — Mr. Gledhill described the streaks a, /3, rj, and y as 

 seen on the 19 th, but brighter ; he also described the apex of the light- 

 sector as reaching to about spot No. 3 ; he has, further, this remark : — " On 

 the S.W. rim of Plato, near or at the foot of the inner slope, are three bright 

 foci; from these the three great bright streaks on the floor proceed, — (1) a 

 line from the uppermost, on the S. border, produced to N.E., cuts spots Nos. 1 

 and 3 [this must be the streak e] ; (2) a line from the next lower produced 

 passes just S. of spot No. 3 [this is GledhUl's 6] ; (3) a line from the lowest, 

 towards the N.W., cuts the E. border of Plato just below or N. of II E"''^. I 

 could not trace the streaks well which proceeded from these foci. On the same 

 evening, with the Royal Astronomical Society's Sheepshank's telescope No. 5, 

 aperture 2-75 inches, power 100, I observed Plato and found the floor very 

 iU-defined, the sector the only light marking visible ; it was brightest towards 

 the S.E. border. Definition, Earth's atmosphere * very bad, much boiling and 

 fluttering.' The definition on the moon was very irregular ; Plato was very 

 difficult to observe, while the markings around Copernicus and Kepler were 

 admirably seen. I determined the following tints : — the surface aroundKepler 

 = 5°-0 ; Plato, the S.E. part of sector, =4°-8; Mare Imbrium, S. of Plato, 

 »=4°-4 ; Mare Imbrium, between the Mountain Chajorra and Straight chain, 



