1874.] and its Influence on Lunar Questions. 501 
convulsion, a magnificent lunar crater to be formed, and 
cover the surface around with streams of lava, with a mouth 
two thousand yards in diameter and a thousand feet deep, 
its discovery would be improbable—nay, unless it occurred 
close to some few small localities, it is almost certain that 
it would not be detected as a new formation. Assuming, 
however, that one of these new formations were to appear, 
or some craterlet a thousand feet deep and several miles in 
diameter collapse into ruins, and granting one or two of the 
very few astronomers who study the moon’s surface had for 
years sufficiently studied the small portion of surface where 
it occurred as to be sure it was a new formation, it would 
then be found impossible to prove it to other astronomers. 
The actual effects of libration on the moon, in ever 
presenting the objects on its surface in new lights and at 
different angles, makes the lunar formations always variable 
in appearance to some extent ; while the general opinion of 
the powers of libration to change the appearance, visibility, 
and form of lunar objects, even near the lunar centre, is such 
that the most marked changes of appearance are ascribed to 
its effects. It would therefore require a most striking and 
wonderfully marked difference in the appearance of a large 
lunar formation to occur, before the existence of lunar 
volcanic, or other inherent energies would be admitted as 
demonstrated, or perhaps probable. There is, in fact, a 
certain amount of basis for this reluctance to admit the 
existence of lunar changes, for certainly the difficulty in the 
study of the details of the moon’s surface is such as to render 
great caution necessary; but it must not be overlooked, as is 
commonly done, that this in itself prevents the absence of 
any proved case of change in the lunar formations being 
accepted as a complete demonstration of the cessation of the 
action of all volcanic and similar forces on the surface of the 
moon. 
Those astronomers who have made the details of the 
surface of the moon their study, are well acquainted with 
the almost absolute want of knowledge of the real minute 
details of the surface, and accordingly have long been 
convinced, with perhaps the exception of Beer and Madler, 
that we are without any evidence of the constancy of the 
configuration of the moon’s surface, with one exception, and 
this bar to the possibility of the moon’s volcanic and other 
sub-lunarian energies being still actively at work was the 
supposed absence of an atmosphere. Volcanic a¢tion and 
no atmosphere seems inconceivable, as De la Rue has long 
remarked, but, grant the existence of the lunar atmosphere, 
VOL. IV. (N.S.) 38 
