Royal Society. 143 



these, which are more suited to the general reader, the volume be- 

 fore us differs in kind ; and those who desire to be really acquainted 

 with the minuter details of the various regions treated of will find 

 that Mr. Birt's work treats of these especially. Herein it is unique, 

 and contains a mass of valuable information to be met with, so far 

 as we know, in no other work extant. Indeed all Mr. Birt's maps 

 and notes are distinguished by a painstaking accuracy that will con- 

 fer upon them great value should another case arise Similar to that 

 of Linne in any of the areas already completed ; for there will be 

 found every known spot, streak, craterlet, or other feature de- 

 scribed, and often distinctly illustrated ; so that, so far as this 

 work is concerned, no future selenographer will be likely to be 

 misled. 



Another portion of the volume is occupied by two series of 

 papers, entitled " Selections from the Portfolios of the Editor of 

 the Lunar Map and Catalogue," in the preparation of which Mr. 

 Birt has been assisted by gentlemen who have given some attention 

 to selenography, and in which will be found many very interesting 

 papers. Especially noticeable is one by the Rev. T. W. "Webb, 

 " On the Study of Change in the Lunar Surface," and another by 

 Messrs. Webb and Birfc on the formation named Cleomedes. The 

 latter contains formulae for computing the length of a measured 

 line on the moon's surface in English feet, in itself a really impor- 

 tant acquisition to every selenographer. Many other papers, treat- 

 ing of various topics, will be found suggestive. 



Erom a notice on the wrapper of the second issue of the " Selec- 

 tions," we learn that increased subscriptions are required to con- 

 tinue them. But we cannot suppose that the want of subscriptions 

 is dependent upon any inferiority in the work itself, but rather on 

 its being not generally known amongst astronomers, and also on 

 the absence of an interest in the study of the moon's surface, which 

 contrasts so remarkably with the assiduity with which amateurs 

 prosecute their studies in other branches of astronomy. We there- 

 fore hope that before long we shall be called upon to notice a fur- 

 ther contribution to selenography by Mr. Birt. 



XXIV. Proceedings of Learned Societies. 



ROYAL SOCIETY, 

 [Continued from p. 72.] 



January 29, 1874. — Joseph Dalton Hooker, C.B., President, in 

 * the Chair. 

 r PHE following communication was read: — 

 -*- " On the Comparative Value of certain Geological Ages (or 

 groups of formations) considered as items of Geological Time." 

 By A. C. Ramsay, LL.D., V.P.B.S. 



The author first reviews briefly several methods by which 

 attempts have been made to estimate the value of minor portions 



