70 REPORT— 1871. 



of the slope is still dusky. The shadow of the N.E. component of No. 3 is 

 easy, and lies to the N^.E. A line from the lower edge of the shadow in the 

 great gap of the west border along the lower edge of the central shadow 

 goes into the gap at the N. end of II E'l'^. This shadow is now finely bifur- 

 cated ; the lower or northern peak is the longer. 



8'\ Spot No. 1 is now seen as a large striking object. It seems to be in 

 the path of the upper fork of the central shadow, and looks like the shadow 

 of one of Jupiter's satellites on the disk. [In Mr. Birmingham's sketch of 

 May 19, 1869, ©— S8 =286° 37'-3, the upper or southern fork of the central 

 shadow is longest, while in the present series of observations the northern is 

 the longest. This is not a solitary instance of variation in the shadow of this 

 peak. Mr. Birmingham is in agreement with Mr. GledhiU in referring spot 

 No. 1 to the upper or southern fork. In my paper on the spots and shadows 

 of Plato (Transactions of Sections, p. 17, ' Report of British Association for 

 the Advancement of Science,' 1869), I remark that Rosse and Birmingham 

 have drawn No. 1 with the shadow of Z just receding from it. ChaUis's 

 shadow of h terminates by a straight line ; neither fork was visible, for he 

 carefully measured the two angular points. Rosse di'ew the termination of 

 the shadow as from two pinnacles upon the summit, with No. 1 between 

 them. These variations are doubtless azimuthal ; nevertheless they are of 

 great importance, as we hoi^e presently to show.] 



8*^ 5'". Spot No. 1 is a large, lofty, very prominent cone. Close to the N.E. 

 component of No. 3, and to the N.E. of it, is seen a black shadow curved to 

 the N.E., with a bright elevated object close to the curve. I see the two 

 components of No. 3 as bright distinct objects ; then, close to the N.E. foot 

 of the N.E. component, comes a large circular shadow quite black, embracing 

 a bright object to the N.E. 



8*^ 15™. Spot No 4 is already getting rather difficult and hazy, although it 

 lies far away in the bright eastern floor. Spot No. 17 is now seen just ou 

 the lower edge of the uppermost pointed shadow. No. 1 is bright aud large, 

 free from the long shadow. Shadow still lies on the eastern floor at the foot 

 of the slope. Mr. Pratt, the same evening, Jan. 10, noticed a peculiar feature 

 of the eastern part of the floor corroborative of Mr. Gledhill's observation of 

 the dip to the foot of the east border. He says, " A peculiar feature of the 

 eastern part of the floor in sunhght observed. Between what was probably 

 the eastern margin of the sector h and the foot of the interior slope of the 

 E. rim was a decidedly darker tint, as if that part of the floor was lower 

 than the rest, and perhaps falling towards the border ; the western margin 

 followed very closely the form it would have if the whole space between the 

 sector b and the border were depressed." In my own record, Jan. 10, 4*^ 48"', 

 the Crossley equatorial 7"3-in. aperture, eye-piece No. 4, power 122, with 

 slot, I say : — " The S. spire of sunlight apparent ; it is directed towards the 

 middle of II E'''^. Neither of the spires of light reach the border, indicating 

 the floor to dip near the border." 



Mr. GledhiU summarizes his observations, under the head of " points de- 

 termined," as follows : — 



First. The position, size, alignment, and order of development of tlic 

 streaks [of sunlight, as distinguished from those that make their aj^pear- 

 ance afterwards] which first fall on the floor. They are evidently the solar 

 rays passing through the gaps on the border. 



Second. The floor on the E. at the foot of the inner slope lies in shadow 

 more or less deep until the giant shadows from the W. border have retreated 

 westward beyond the centre of the crater. 



