26 Evolution by Expansion. [January, 
The instances that have been dealt with in the preceding 
pages will show that selenographers are not without strong 
evidence in favour of the opinion that has long been unani- 
mously held by them, that processes of change are still 
actively at work upon the moon. It must not, however, be 
supposed that the above are the sole instances which they 
have recognised, because this is by no means true, only the 
difficulties in establishing others have led to their omission 
here. Dealing with a subject such as Selenography, it is 
only those who are familiar with all its details who properly 
appreciate the evidence in favour of or against its problems, 
- — just as in the branches of mathematical astronomy, dealing 
with our satellite, it is only a proficient in mathematical 
astronomy who could appreciate the difficulties of the lunar 
theory, and feel a true confidence in the correctness of the 
manner in which they have been overcome. The difficulties 
in the way of making the true bearings of selenographical 
questions properly understood are greater than might be 
imagined ; for even the very elementary faCt that volcanic 
changes such as are now active on the earth would not be 
recognisable on the moon, in the present state of our 
acquaintance with the configuration of its surface, is not 
generally understood. When, however, the attention of 
astronomers is more generally directed to the study of the 
lunar surface, Science will be greatly the gainer, as it is 
there that the past and future of our earth is to be learnt. 
II. EVOLUTION BY EXPANSION, 
VERSUS 
EVOLUTION BY NATURAL SELECTION. 
By J. Huddart. 
S HERE is nothing more difficult than to disembarrass 
the mind of a preconceived idea. A belief instilled 
in childhood and entertained through life, without a 
shadow of suspicion as to its truth, takes such firm hold of 
the imagination as positively to unfit the reason to judge 
impartially of any opinion opposed to that belief, however 
false and monstrous it may be. 
