e, indeed, of similar appearances under circumstances less
amenable to explanation inclined Webb to the view that effusions of
native light actually occur.[929] More cogent proofs must, however, be
adduced before a fact so intrinsically improbable can be admitted as
true.

But from the publication of Beer and Maedler's work until 1866, the
received opinion was that no genuine sign of activity had ever been
seen, or was likely to be seen, on our satellite; that her face was a
stereotyped page, a fixed and irrevisable record of the past. A profound
sensation, accordingly, was produced by Schmidt's announcement, in
October, 1866, that the crater "Linne," in the Mare Serenitatis, had
disappeared,[930] effaced, as it was supposed, by an igneous outflow.
The case seemed undeniable, and is still dubious. Linne had been known
to Lohrmann and Maedler, 1822-32, as a deep crater, five or six miles in
diameter, the third largest in the dusky plain known as the "Mare
Serenitatis"; and Schmidt had observed and drawn it, 1840-43, under a
practically identical aspect. Now it appears under high light as a
whitish spot, in the centre of which, as the rays begin to fall
obliquely, a pit, scarcely two miles across, emerges into view.[931] The
crateral character of this comparatively minute depression was detected
by Father Secchi, February 11, 1867.

This is not all. Schroeter's description of Linne, as seen by him
November 5, 1788, tallies quite closely with modern observation;[932]
while its inconspicuousness in 1797 is shown by its omission from
Russell's lunar globe and maps.[933] We are thus driven to adopt one of
two suppositions: either Lohrmann, Maedler, and Schmidt were entirely
mistaken in the size and importance of Linne, or a real change in its
outward semblance supervened during the first half of the century, and
has since passed away, perhaps again to recur. The latter hypothesis
seems the more probable: and its probability is strengthened by much
evidence of actual obscuration or variation of tint in other parts of
the lunar surface, more especially on the floor of the great "walled
plain" named "Plato."[934] From a re-examination with a 13-inch
refractor at Arequipa in 1891-92, of this region, and of the Mare
Serenitatis, Mr. W. H. Pickering inclines to the belief that lunar
volcanic action, once apparently so potent, is not yet wholly
extinct.[935]

An instance of an opposite kind of change was alleged by Dr. Hermann J.