308 The Past History of our Moon. (July, 
unlike that presented by the moon. Grant that after the 
lapse of enormous time-intervals the oceans now existing on 
the earth will be withdrawn beneath her solid crust, and 
even (which seems incredible) that at a more distant future 
the atmosphere now surrounding her will have become 
greatly reduced in quantity either by similar withdrawal or in 
any other manner, yet the surface of the earth would present 
few features of resemblance to that of the moon. Viewed 
from the distance at which we view the moon there would 
be few crateriform mountains indeed compared with those 
on the moon; those visible would be small by comparison 
with lunar craters even of medium dimensions; and the 
radiated regions seen on the moon’s surface would have no 
discernible counterpart on the surface of the earth. The 
only features of resemblance, under the imagined conditions, 
would be probably the partially flat sea bottoms (though 
these would bear a different proportion to the more elevated 
regions) and the mountain ranges, the only terrestrial 
features of volcanic disturbance which would be relatively 
more important than their lunar counterparts. 
I do not purpose, however, to discuss the probable future 
of the earth, having only indicated the differences just 
touched upon, in order to remind the reader at the outset 
that we have not in ‘“‘the moon”’ a representation of the earth 
at any stage of her history. Other and different relations 
are presented for our consideration, although it may well be 
that by carefully discussing them we may learn somewhat 
respecting our earth, as also respecting the past history and 
future development of the solar system. 
I have already, on two occasions, discussed in these pages 
some of the problems presented by the observed condition 
of the moon’s surface, and in my treatise on the moon, I 
have in several places indicated the views towards which 
my study of the subject tended. But I have not attempted 
to present any general theory on the subject, feeling, indeed, 
that it was one which presented too many difficulties to be 
hastily dealt with. It seems to me, however, that the enun- 
ciation by Messrs. Nasmyth and Carpenter, of somewhat 
definite theories respecting the moon’s surface, affords me a 
favourable opportunity for advancing considerations which 
I have had much in my thoughts during the last five or six 
months, and which appear to me to accord more satisfactorily 
with observed lunar appearances on the one hand as well as 
with known terrestrial and probable cosmical relations on 
the other, than the theories advanced in the treatise above 
referred to. 
