II 
1 877.] Physical Changes upon the Moon's Surface . 
that a part which is darker than another with one oblique 
illumination will be lighter under another and but slightly 
different illumination. 
“ It appears to me that no other explanation can reason- 
ably be suggested, because, in point of fadt, we have to 
choose between the theory that there has been a definite 
change of surface on this part of the moon, or that the 
change is only apparent. Now, if there has been a definite 
change at any time, fresh changes must have restored, either 
from time to time or definitely, the former condition of the 
surface. But this seems extremely unlikely, whilst such a 
change as Sir John Herschel considered to afford the best 
explanation of Schmidt’s observation may be regarded as 
one which no subsequent process could so modify as to 
restore, or nearly restore, the original appearance of the 
region.” (This explanation of Sir John Herschel’s referred 
to was that the crater of Linne had been filled up to over- 
flow with viscous lava.) “ Such a change would doubtlessly 
account well for the observed appearances, but it leaves the 
subsequent restoration of the crater unexplained.”- — • 
(Pp. 5 °°> 5 01 -) 
From the above quotation Mr. R. A. Prodtor would appear 
to consider that the entire known observations that have 
been made of Linne can be explained by supposing the sur- 
face to vary in tint with differences of illumination, and he 
also seems to suppose that of late years Linne has been 
seen to present the same appearance and possess the same 
charadters as it was described as having before the supposed 
change occurred. But it has been already shown that this 
is entirely a misconception : whatever change occurred in 
Linne was definite, and since 1867 Linne has never been seen 
to accord with the description of the early selenographers. 
To suppose the minute crater-like formation now existing on 
the site of Linnd can be in any manner identical with, or 
even similar to, the twenty times larger formation that was 
observed, drawn, and measured by Lohrmann, and Beer and 
Madler, is out of the question. Nor will any selenographer 
allow that differences of illumination, of any kind or on any 
surface, are capable of explaining the difference in appear- 
ance of the formation at the two different epochs. No 
alteration in illumination whatever could make an objedt 
where Linne is placed look at one period like a considerable 
and deep crater, and at another as a small, scarcely visible 
crater. The means by which Mr. R. A. Prodtor would ex- 
plain the supposed change in Linne are perfedtly inadequate. 
Nor will the effedt of variation in illumination even account 
for the minor variations which it has been supposed have 
