I io ROUGH WAYS MADE SMOOTH. 



ing the conical hole now existing in the Sea of Vapours 

 has given way at last under the effect of long-continued pro- 

 cesses of expansion and contraction, which would operate 

 with special energy over a region, like the Sea of Vapours, 

 near the moon's equator. 



But there remains to be mentioned a form of evidence 

 respecting lunar features which could not be effectively 

 applied to the case of the crater Linne, because the moon 

 had only been subject to the necessary method of examina- 

 tion during a few years before that crater was missed. I 

 refer to lunar photography. Many objects less than two 

 miles in diameter are shown in the best photographs of our 

 satellite by Rutherfurd, De la Rue, Ellery, and Draper ; and 

 as the moon has been photographed in every phase, some 

 among the views might fairly be expected to show Klein's 

 crater if it really existed before 1877. I do not find that 

 in any lunar photographs the crater is shown as a black or 

 dark gray spot. But in Rutherfurd's splendid photograph of 

 the moon on March 6, 1865 (when the moon was about nine 

 days five hours old), the place of Klein's crater is occupied 

 by a small spot lighter than the surrounding ' sea.' This is 

 the usual appearance of a small crater under a high sun ; 

 and though it may indicate only the existence of a flat crater 

 floor in 1865 where now a great conical hole exists, it throws 

 some degree of doubt on the occurrence of any change at all 

 there. The case strongly suggests the necessity for contin- 

 uing the work of lunar photography, which seems of late years 

 to have flagged. Photographs of the moon should be taken 

 in every aspect and in every stage of her librational swayings. 

 Possessing such a series, we should be able to decide at once 

 whether any newly-recognised crater was in reality a new 

 formation or not. 



