Notices respecting New Books. 305 



Z _ M. 

 sin</)~ 6^ 



.•.§(/)= -(5m- 2e)4 



= - I - ?/i — € I Sill Z(p ; 



or, if ^' and g be the values of gravity at the pole and at the 

 equator respectively, then, making use of Clairaut's theorem, 



-'^ 9'-- 9 



3^=-.^^^— ^^sin2<^. 



^ c g 



This result is certainly remarkable for its simplicity ; but, prac- 

 tically, for ordinary mountain-heights it only amounts to a 

 small fraction of a second. 



XL I. Notices respecting New Boohs. 



An Elementary Treatise on the Dynamics of a System of R'lyid Bodies. 

 With Numerous Examples. By Edward John Eouth, M.A.^ 

 F.R.S., F.R.A.S., F.G.S., 4'0., late Fellow and late Assistant Tutor 

 of St. Peter s College, Cambridge ; late Examiner in the University 

 of London. Third Edition, Revised and Enlarged. London : 

 Macmillau and Co. 1877. (8vo, pp. 564.) 



ME. EOUTH'S Treatise on Eigid Dynamics has been for several 

 years the Text Book commonly used by students who " take 

 up " that branch of mechanical science ; so that it may be presumed 

 that those who have paid any attention to the subject, are more or 

 less acquainted with one or other of the earlier editions. The 

 present edition, the third, appears in a different form from those 

 which preceded it, and has been very considerably enlarged. La 

 fact, when both the size of the pages and their number are taken 

 into account, we shall not be far wrong in stating that it is larger 

 by one half than the second edition. So that it is a very large 

 volume; and, further, it contains much more matter than the mere 

 number of the pages might lead one to expect. 



The work is designed to meet the wants of two classes of 

 students — those who wish for information on the higher parts of 

 Dynamics, and those " to whom the subject is entirely new." The 

 parts to which the attention of the latter class should be directed 

 are indicated by a selection of articles comprising about a third of 

 the volume. The remaining two thirds contain most of the addi- 

 tions. The author's aim in making these additions has been to 

 giA^e the student at least some notion of the most important appli- 

 cations of the general doctrines of Dynamics to particular cases ? 

 so that, although such a subject as rigid dynamics might at first 

 sight be thought to be contained within narrow limits, yet in 

 reality the author has had to deal with an extensive literature of 



Phil Mag. S. 5. Vol. 4. No. 25. Oct. 1877. X 



