1 877.] Physical Changes upon the Moon's Surface. 7 
during the next month, by Buckingham and Knott. It must 
be remembered, however, that this crater was only seen when 
the region was very obliquely illuminated by the sun, at 
sunrise or sunset in fadL At any other period all that was 
seen was a white cloudy marking, about 8 miles in diameter. 
Since 1868, it is only on three or four occasions, when the 
atmosphere has been exceptionally good, that the small crater 
within Linne has been seen, and then only in powerful tele- 
scopes. It does not seem ever to have been seen as a distinct 
crater in telescopes as small as those employed by the earlier 
selenographers, who only knew the crater as a fine, distindt, 
conspicuous objedl, with a black interior, nearly five times 
the diameter of that of the present crater. The present dia- 
meter of the crater opening of the cone on the site of Linne 
is about ij miles, the total diameter of the cone at the sum- 
mit about half as much again, and at the base about 
z\ miles. The height above the surface is about 200 feet 
at most. 
As a crater, in fadt, Linne is now one of the most difficult 
to see on the entire Mare Serenitatis. Under illumination, 
when every other crater stands out boldly as distindb objedts, 
Linne is, with rare exception, either invisible as an elevation 
or else appears as an insignificant hill. It is questionable 
whether the earlier selenographers could have seen it at all 
under these conditions. It should be mentioned, however, 
that between 1867 and 1869 several observers considered 
that they could detedt traces of the ring of a very shallow 
crater around the crater cone in the position of Linnd, and 
in size slightly larger than the crater of Beer and Madler. 
The adfual existence of this ring is doubtful ; it has not been 
seen since 1869, and the appearance noticed probably arose 
from a number of ridges and mounds near the position of 
Linne. 
Considering, then, the fadts as stated above, it would 
appear that there could be no question but that a real phy- 
sical change had occurred on this portion of the surface of 
the moon. The large crater independently described by 
Lohrmann, Beer and Madler, and Schmidt, as existing in 
this portion of the Mare Serenitatis, unquestionably no 
longer exists, and in its place appears a white cloudy 
marking, containing a small crater cone, with an opening 
scarcely one-twentieth of the area of the former crater. 
What reasons have therefore been advanced against any 
change having taken place, that astronomers in general 
should favour this view ? The principal reason why astro- 
nomers are so strongly against allowing that any change can 
