5 
i8 77.] Physical Changes upon the Moon's Surface . 
tions, that the others, not thus acquainted with these 
features, refuse to accept. The purport of the present paper 
is to detail instances of what selenographers consider to be 
real physical changes in the moon, together with some of 
the reasons which they have for supposing them to be such. 
From an opposite point of view the subject has been already 
ably handled in these pages by one of our most eminent 
astronomers, Mr. R. A. Prodtor, who in his own department 
of the science stands still unrivalled.* 
The most prominent instance of a supposed change on 
the surface of the moon is indubitably that of Linne, be- 
cause it is an instance which was brought before the entire 
astronomical world, and engaged for nearly a year the atten- 
tion of almost every astronomer in Europe. The leading 
fadts of the case may be briefly stated as follows -On the 
north-west quadrant of the moon is a large tradt of nearly 
level surface, of a pale grey, almost greenish colour, and 
this region — which is in extent about 430 miles in diameter 
— contains near the centre a moderate-sized bright crater, 
called Bessel, nearly 14 miles in diameter, and with a circular 
wall rising 4000 feet above the interior and about 1600 feet 
above the surrounding surface. Scattered about this plain 
are a few small crater-like objedts, about 2J miles in diameter 
and with walls rising about 300 feet high. Now, near the 
eastern centre of this great tradt of level ground, or the 
Mare Serenitatis as it is called, one of the most eminent 
selenographers, Lohrmann, had placed a distindt bright 
crater, subsequently called Linne, and this crater he described 
as being about 5 miles in diameter, and, after Bessel, the 
most conspicuous objedt on the Mare Serenitatis. Ten years 
later our greatest selenographer, Baron von Madler, con- 
firmed Lohrmann’s description, and named the crater Linne, 
which he described as deep and very distindt in oblique 
illumination. He measured its diameter, which was 6j miles, 
or about half the size of the great crater Bessel, and seledted 
it as the most distindt objedt in its region, for one of the 
measured units in his great trigonometrical lunar survey. 
Now, had Lohrmann’s account not been corredt, Madler 
would certainly have been struck at once by the fadt ; but 
Madler’s work, which was entirely independent of his pre- 
decessor, entirely confirms the account. And had Madler’s 
account been incorredt, the instance would have been so 
evident that it could not have escaped the attention of 
Gruithuisen and Schmidt, who were about this time making 
*' Quarterly Journal of Science, January, 1873, and Odtober, 1873. 
