OBSERVATIONS OF LU^fAR OBJECT.iS. 



263 



divide it iato two separate streaks, that east of spot No. IG being designated 

 " a," the western part " o." On October 19 Mr. Glodhill delineated it as a 

 narrow streak (see fig. 17, p. 238) ; but as he omitted the western part of the 



Fig. 8. 



Fig. 9. 



Plato, 1839, Sept. 2a.— T. G. E. Elger. 



Plato, 1839, Sept. 25.— J. aiedhill. 



floor it is uncertain if the continuation reached the border. On the 21st it was 

 recorded as brighter than on the 19th. On the 25th a dark space was seeu 

 between it and the border ; and it was observed by Mr. Gledhill on. the 26th 

 and on the 27fch, in the interval between 12 hours and sunset. 



Lunation November 18Q9,froni 111 hours before to 21 hours after meridian. 



On November 14, at an earlier epoch than it had hitherto been observed, 

 Mr. Gledhill recorded the streak as seen east of spot No. 16, the western 

 part " " being absent. On January 12 Mr. Elger (same interval, 60 to 72 

 hours) showed in his drawing the continuation " o," with an extension of its 

 north-west border to the north-west border of Plato, i. e. the floor from the 

 south-east border of " o " to the rim of the crater was equally bright ; this 

 brightness commenced on the east at "Webb's elbow. On the 19th of No- 

 vember the continuation " o " was observed contemporaneously with c, which 

 reached nearly to S, and was convex towards the border. This is in contrast 

 with later observations, in which c was seen concave towards the border 

 (see lunation April 1870, 2}ost, p. 264). The contemporaneity of c and " o " 

 indicates that a change had supervened between the first observation in 

 September and November 19, on which day Mr. Gledhill recorded a as tho 

 hrirjhtcst streak on the floor, and first observed Webb's elbow. 



Lunation December 1869, from interval 24 to 36 hours after sunrise to interval 



48 to 36 hours before sunset. 



This lunation aflbrded as many as ten observations of Plato, so that the 

 progression of the illumination of the streak could be well traced. At first, 

 on the 12th, it was seen with difficulty, the north-Avest part of the floor being 

 brightest. On the 13th it was still difficult to separate from the north and 

 north-west part of the floor ; but on the 14th it was seen continued in " o," 

 the two forming the brightest and best-defined streak on the floor. Interval 

 72 to 84 hours. The observations of December 12 and 13 are the earliest of 

 the bright north-west floor, which would, from its dip towards the border, 

 reflect more light soon after sunrise than at a later period of the luni-solar 

 day; and it may have been from this circumstance that the brightness of 

 the streak merged into that of the floor. It is, however, noteworthy that on 

 February 9, 1870, interval 24 to 36 hours after sunrise, the streak a should 



