Klein of Cologne in March, 1878.[936] In Linne the obliteration of an
old crater had been assumed; in "Hyginus N.," the formation of a new
crater was asserted. Yet, quite possibly, the same cause may have
produced the effects thought to be apparent in both. It is, however, far
from certain that any real change has affected the neighbourhood of
Hyginus. The novelty of Klein's observation of May 19, 1877, may have
consisted simply in the detection of a hitherto unrecognised feature.
The region is one of complex formation, consequently of more than
ordinary liability to deceptive variations in aspect under rapid and
entangled fluctuations of light and shade.[937] Moreover, it seems to be
certain, from Messrs. Pratt and Capron's attentive study, that "Hyginus
N." is no true crater, but a shallow, saucer-like depression, difficult
of clear discernment.[938] Under suitable illumination, nevertheless, it
contains, and is marked by, an ample shadow.[939]

In both these controverted instances of change, lunar photography was
invoked as a witness; but, notwithstanding the great advances made in
the art by De la Rue in this country, by Draper, and, above all, by
Rutherford in America, without decisive results. Investigations of the
kind began to assume a new aspect in 1890, when Professor Holden
organised them at the Lick Observatory.[940] Autographic moon-pictures
were no longer taken casually, but on system; and Dr. Weinek's elaborate
study, and skilful reproductions of them at Prague,[941] gave them
universal value. They were designed to provide materials for an atlas on
the scale of Beer and Maedler's, of which some beautiful specimen-plates
have been issued. At Paris, in 1894, with the aid of a large "equatoreal
coude," a work of similar character was set on foot by MM. Loewy and
Puiseux. Its progress has been marked by the successive publication of
five instalments of a splendid atlas, on a scale of about eight feet to
the lunar diameter, accompanied by theoretical dissertations, designed
to establish a science of "selenology." The moon's formations are thus
not only delineated under every variety of light-incidence, but their
meaning is sought to be elicited, and their history and mutual relations
interpreted.[942] Henceforth, at any rate, the lunar volcanoes can
scarcely, without notice taken, breathe hard in their age-long sleep.

Melloni was the first to get undeniable heating effects from moonlight.
His experiments, m