1 ^>73'] Changes in the Moon's Surface. 509 



Still less would I have it thought that such researches as 

 those which Mr. Birt has advocated, and to some degree 

 prosecuted, should be discontinued as useless. On the 

 contrary, I consider in the first place that they have already 

 led to results which, however interpreted, are of great 

 interest and importance, and that in the second they 

 are the only possible means for arriving at a solution 

 of the problems suggested by the general aspect of our 

 satellite. 



What I wish, however, to urge earnestly on students of 

 the moon is the necessity of perfect independence of pre- 

 conceived opinions as they proceed in their enquiries. The 

 results they obtain should not be held to owe their importance 

 to the evidence they seem to give in favour of this, that, or 

 the other theory, but should be discussed altogether without 

 bias for one view or another. If in this essay I have 

 given prominence to the objections which may be urged 

 against the evidence thus far obtained, so far at least as it 

 has been regarded as evidence of real change, it is solely 

 because, in my judgment, this is necessary to correct a 

 contrary tendency on the part of those who consider that 

 real changes have been demonstrated. I shall venture to 

 quote, in conclusion, the words of a well-known student of 

 the moon, who, if he inclines somewhat (as his words will 

 show) to the theory that change has taken place, nevertheless 

 presents very fairly the doubts which really surround the 

 whole subject. Thus, then, speaks the Rev. Mr. Webb, after 

 describing some of the principal causes of deception by 

 which changes of illumination, or of direction of vision 

 may affect the aspect of lunar regions : — 



" It would be easy to extend this list of causes of decep- 

 tion ; but those here given may suffice as indications of the 

 caution with which it is necessary to approach the much 

 disputed question of still existing physical change. In 

 the answer to that question — the affirmative answer — 

 undoubtedly lies a great part of the charm of selenography. 

 Whatever may be the magnificence of the abrupter features 

 of the lunar scenery, or the smooth and tranquil aspect 

 of its gentler valleys and wide-extended plains, we shall 

 contemplate them with a different amount of interest 

 accordingly as we are obliged to consider them an inanimate 

 and silent record of the worn-out and spent convulsions of 

 bygone ages, and forces wholly extinct in selenological 

 death ; or whether we may detect if it be but the last feeble 

 efforts of that marvellous working which once threw open 

 such amazing gulfs, and piled up such terraces and towers 



VOL. in. (n.s.) 3 u 



