316 The Past History of our Moon. (July, 
existed at that time it would occupy the depressed regions 
which at the present time are called Maria or Seas. Itisa 
question of some interest, and one on which different 
opinions have been entertained, whether the moon at any 
stage of its existence had oceans and an atmosphere corre- 
sponding or even approaching in relative extent to those of 
the earth. It appears to me that, apart from all the other 
considerations which have been suggested in support of the 
view that the moon formerly had oceans and an atmosphere, 
it is exceedingly difficult to imagine how, under any circum- 
stances, a globe so large as the moon could have been formed 
under conditions not altogether unlike, as we suppose, those 
under which the earth was formed (having a similar origin, 
and presumably constructed of the same elements), without 
having oceans and an atmosphere of considerable extent ; 
the atmosphere would not consist of oxygen and nitrogen 
only or chiefly, any more than, in all probability, the primzval 
atmosphere of our own earth was so constituted. We may 
adopt some such view of the moon’s atmosphere—mutatis 
mutandis—as Dr. Sterry Hunt has adopted respecting the 
ancient atmosphere of the earth. Hunt, it will be remem- 
bered, bases his opinion on the former condition of the earth 
by conceiving an intense heat applied to the earth as now 
existing, and inferring the chemical results. ‘‘To the 
chemist,” he remarks, “‘ it is evident that from such a process 
applied to our globe would result the oxidation of all carbon- 
aceous matter; the conversion of all carbonates, chlorides, 
and sulphates into silicates; and the separation of the car- 
bon, chlorine, and sulphur in the form of acid gases ; which, 
with nitrogen, watery vapour, and an excess of oxygen, 
would form an exceedingly dense atmosphere. The resulting 
fused mass would contain all the bases as silicates, and 
would probably nearly resemble in composition certain 
furnace-slags or basic volcanic glasses. Such we may con- 
ceive to have been the nature of the primitive igneous rock, 
and such the composition of the primeval atmosphere, which 
must have been one of very great density.” All this, with the 
single exception of the italicised remark, may be applied to 
the case of the moon. The lunar atmosphere would not 
probably be dense at that primeval time, even though con- 
stituted like the terrestrial atmosphere just described. It 
would perhaps have been as dense, or nearly so, as our pre- 
sent atmosphere. Accordingly condensation would take 
place at a temperature not far from the present boiling- 
point, and the lower levels of the half-cooled crust would be 
drenched with a heated solution of hydrochloric acid, whose 
