13 KEFOKT 1867. 



opinion as to change. Varying angles of ilhimination appear to affect objects 

 on the moon's surface differenthj ; for example, under an oblique illumination, 

 when the sun shines more directly on the steep sloping sides of some craters, 

 they appear very bright ; this brightness arises from two circumstances, viz. 

 the nature of the surface of the sloping sides, and the angle of illumination 

 upon them being more direct ; this of itself -will make a difference in the 

 brightness (when no real difference exists in the reflective power of the in- 

 terior and exterior surfaces) at the times of sun-rising and setting ; as the 

 sun rises higher above the horizon the brilliancy from this cause declines. 

 The variations in the brilliancy of Linnc, y Posidonius, and other spots which 

 arc similarly affected, do not appear to be produced in the same manner. 

 The difference arising from elevation in the case of Linnd (if it exists) seems 

 to be too slight to occasion any appreciable effect. The gradual brightening 

 of such spots as Linne, especially when situated on a ground which darkem 

 ujider the more direct rays of the sun, appears to point to something in the 

 nature of the surface of the spot — as contrasted with that of the surrounding 

 surface — on which the sun's rays exert an influence, rendering it, for the time 

 being, capable of reflecting a greater amount of light. While there is a more 

 or less constant relation between reflective power and angle of illumination, 

 the recorded differences of reflective power under the same angles of illumina- 

 tion, would indicate that these differences depend upon other circumstances 

 than increase and decrease of illuminating angle. The phenomena presented 

 by Linnc during the last twelve months are strikingly in contrast with those 

 presented by Plato, as observed by me between 1859 and 1863. Linne is 

 faint under "oblique rays, bright under those that are more direct. Plato re- 

 flects more light under oblique, and less under more direct rays, i. e. the sur- 

 face is of a darler tint under a higher angle of illumination. 



The Shaliow Ckatee. 



This object, of which no measures exist, has not been previously recorded, 

 unless SchriJter's description of the spot v refers to it (see ante, pp. 3 & 4). 

 His language is, however, rather ambiguous, and it is doubtful as to whether 

 he describes a plain on the same level as the adjacent surface of the Mare 

 Serenitatis, or one bounded by a low wall which did not rise above the sur- 

 rounding level. It appears that he did not determine the precise natiire of 

 the spot V. Schrciter's description is quite irreconcileable with the appearance 

 of Linne as given by Lohrmann and by Beer and Miidler. 



Observations of the Shallow Crater. — These have been but few, as 

 under : — 



1. 1867, Jan. 12. Mr. Kxott, 7.^ Alvan Clark, Dawes's eyepiece, powers 

 14.5 and 240, saw the " Ghost " of the ring of Linne. His observation is 

 recorded as foUows, January 12, 6"^ 40'» to 7" 15"', G. M. T. :— 



" I saw clearly the ' Ghost' of the ring of Linne. * * * It is broader (and 

 brighter?) on the western side. The shading in the interior is of about equal 

 intensity with that of the surrounding Mare. I do not see any real interior or 

 exterior shadow, though the shadows in neighbouring craters, even those of 

 very small dimensions, are very distinct. The ring or wall of the crater has 

 a slightly nebulous appearance, and is in brightness barely equal to that of 

 the knoll on the Mare east of Posidonius, marked y on B. etM.'s large map. 

 Its diameter is, to my eye, less than that of Sulpicius Gallus." — Astronomi- 

 cal Eegister, No. 50,"Feb. 1867, p. 33. 



2. Jan. 12. Mr. Buckixgham saw, in moments of quiet air and good de- 

 finition, " a very shallow depression all over the enlightened spot of Linne, 



