3 
i877*1 Physical Changes upon the Moon’s Surface. 
whatever that there is no atmosphere of the nature sup- 
posed.* 
It would be an interesting inquiry to ascertain in what 
manner arose this direct conflict of opinion on this 
subjedh, between those who have systematically studied the 
appearances presented by the moon, and those who have 
not in the same systematic and assiduous manner examined 
the lunar surface. It appears to have originated in a short 
summary by Madler of the appearances presented by 
the moon, wherein the differences between the condition of 
the moon and earth were forcibly stated, and where he 
pointed out the impossibility of the view that was held in 
the time of the earlier astronomers, — that the moon might 
be a mere copy of the earth, containing a dense atmosphere, 
large oceans, abundant vegetation, and animal life, or even 
human inhabitants. In a condensed and more unqualified 
form these remarks crept into all astronomical text-books, 
and were the main basis of the views commonly held by 
astronomers. 
The present condition of this question is therefore not 
surprising; with the views of those astronomers who have 
devoted many years to the study of the moon, but very im 
perfectly known, and in fadt inaccessible to most astro 
nomers, the general body of observers are left to draw their 
own conclusions from their own acquaintance with the lunar 
* The subjedt of the phenomena which would be presented by the moon 
were it surrounded by an atmosphere of any given density is one of very con- 
siderable difficulty. It cannot be treated in a popular — and therefore necessa- 
rily superficial — manner, because it involves subjects demanding a tolerably 
extensive acquaintance with mathematical physics to enable their real bearing 
to be understood. The mathematical treatment of the subjedt, though in- 
volving no point of any particular difficulty, is nevertheless complex and very 
laborious, from its extent. It is not surprising, therefore, that when this sub- 
ject is regarded in a popular manner ideas should be arrived at that a more 
elaborate and careful examination shows, by mathematical demonstration, to 
be mistaken ; and it was in this manner that Bessel, in his investigation of a 
portion of this subjedt, arrived at results which — though they have been since 
shown to be wrong — have exerted the greatest influence on the progress of 
selenography. In saying that there is no real evidence whatever that the 
moon does not possess the atmosphere which has been ascribed to it by the 
author, it must not be supposed that no attention has been paid to the various 
circumstances which have from time to time been pointed out as proving the 
impossibility of the moon possessing an atmosphere of a surface density far 
less than this. But on submitting these objections to the careful examination 
that they demand, and in particular by calculating with the aid of the powers 
of mathematical analyses what would be the real dimensions of these pheno- 
mena which it is supposed would reveal the existence of the lunar atmosphere, 
it is found that, for the atmosphere supposed, they would be insensible. Most 
of these objections have been already considered in my recent work on the 
Moon, or in the “ Quarterly Journal of Science ” (October, 1874). The whole 
subjedt involves such difficulties that statements founded on merely a pnoular 
or general consideration of the problem it involves require therefore to be 
regarded with caution. 
B 2 
