250 Notices respecting New Books, 



ha,vep = a 2 p throughout the motion, it will not be enough that 

 we havej9 = 2 / 2 (<2?) when £=0. We must have 



«V=-j+*("+J> 



Eliminating v+ ~ between this equation and the last two of (2) 



we shall obtain two equations between p, x, and t only, which 

 must needs be identical ; whence it can easily be shown that we 

 must have j <p{u)-* _a , 



D ~D J 

 and therefore <£( w ) =2^ + C. 



6 New Square, Lincoln's Inn, August 7, 1873. 



XXIX. Notices respecting New Books. 



The Mare JSerenitatis : its Craterology and principal features. 



By "W. E. Bikt, F.B.A.S. London : Taylor and Francis. 

 TN the year 1867 Mr. G-laisher, in his report o£ the Lunar Com- 

 -*- mittee of the British Association for the Advancement of Science, 

 has this remark : — " Had the Mare Serenitatis undergone the close 

 scrutiny in the course of this work which the Mare Orisium has in 

 compiling the table in the report presented at Birmingham, this 

 Committee could have pronounced decisively as to the state of Linne 

 a little anterior to the announcement of change by Schmidt." If 

 the present unsettled state of the question of change, especially as 

 regards Linne, be a reproach to Selenography, as it evidently must 

 be when we find a popular writer announcing that an undoubted 

 change in this remarkable crater had really taken place, and then 

 some few years afterwards acknowledging that when he wrote in 

 1867 he " had not an adequate conception of the difficulties of the 

 subject," it becomes exceedingly important that difficulties which 

 tend to retard the progress of our knowledge of the moon's surface 

 should be met in such a way as to reduce controversy to its smallest 

 extent. This Mr. Birt, in the monograph before us, has endeavoured 

 to do by specifying no less than 333 distinct objects on or near 

 the Mare Serenitatis, an extensive lunar plain of more than 400 

 miles diameter. The map, which has been thoroughly revised, 

 contains every object which has been recorded since Hevel's and 

 Eiccioli's epoch to the present ; and students who really wish to 

 contribute to the settlement of the interesting question of change 

 the monograph cannot fail to assist materially. The authority 

 by whom any given object was first recorded is inserted in the 

 table accompanying the map ; and to each object of special interest 

 illustrative notes are appended. By the aid of the monograph in 

 connexion with existing records, the history of any single object 

 can be readily traced, and its existence or non-existence, with any 

 changes it may have undergone, ascertained. 



