ON MAPPING THE SURFACE OP THE MOON. 5 
Athens, 1868, June 5. 
Honovrep Srr,—I have lately given attention to a region of the moon 
which deserves in future a more accurate investigation. Although it fur- 
nishes by no means so significant a case as was afforded by Linné, it shows, 
however, something analogous, and leads to a better knowledge of certain 
spots of light which cannot in all cases be explained by mere phenomena of 
reflexion. The region in question is situated easterly near Alpetragius, the 
spot of light to which I direct your attention in 12° east longitude and 14° 
‘south latitude =d. Schréter has nothing about it. Lohrmann’s (unedited) 
plate gives a very large spot of light, almost 2° in magnitude, and a very 
small hill inside it. 
Midler draws a crater of almost a mile [4:6 miles English] in diameter, 
and says in his ‘Selenography’ [Der Mond], page 304, line 22 from above, 
«Tn the furthest east shines also with a light of 8° the small crater d.” 
This crater d now no longer exists; but in its place is a round spot of 
light more than 2 miles [9-2 English] broad, extremely brilliant, which has 
quite the character of the light spot Linné, and of the few others of this kind 
which also are found upon the moon. The small neighbouring crater south 
of d which Midler gives is still distinctly visible. 
I have annexed three sketches—the first from Midler, the second from 
Lohrmann, the third my own, on the scale of my chart. 
Will you have the goodness to take an opportunity of informing the Lunar 
Committee of this notice, and request new observations with large instru- 
ments ? 
With the greatest esteem, 
Yours most truly, 
J. F. Juzivs Scumipr. 
Bright spots on the moon are of two kinds, viz. those which are clearly 
and unmistakeably the slopes of mountains or the interiors of craters, and 
those which appear as round nebulous spots, apparently on the moon’s sur- 
face, the true nature of which we are at present ignorant of. The bright- 
ness of the first class depends upon the following conditions, which determine 
the angle of illumination—1° and 2° the sun’s altitude and azimuth at the 
spot, 3° and 4°, the angles which the slope and direction make with the lunar 
horizon and meridian. In the case of each particular spot certain values of 
the above-mentioned angles determine the maximum of illumination, and 
consequently the greatest brightness in the course of the lunar day. The 
bright spots of the second class do not conform to the before-mentioned con- 
ditions. They are apparently horizontal; butit has not yet been ascertained 
by observation whether they are in contact with the surface or otherwise. 
The three spots of this nature which have been most extensively observed 
are Linné [IE”!], Posidonius y [1E® 2; and IV A*!” TV As 9, and these 
present some very remarkable differences. Nearly throughout the whole 
course of the lunar day Linné appears as a white spot, varying slightly in 
brightness, and more so in size; generally it appears as nearly as possible of 
about the same size and brilliancy as Posidonius y, sometimes slightly ex- 
ceeding y, and at other times a trifle less both in size and brightness. Posi- 
donius y is the highest part of a ridge on the Mare Serenitatis, haying on its 
summit a minute pit. Linné, from the latest observations, is a small cone 
on a nearly level portion of the Mare. At and shortly after sunrise both have 
been distinctly seen as well-defined bright spots of the first class. Ata very 
early period of the lunar day Zinné exchanges the characteristics of the first 
