218 Notices respecting New Books. 



Tangent wheel = 180 turns, 

 Each turn = 67, 



180x67 _^ 



127 ~ yi> leSS 127 



Therefore 95 holes of the 67 wheel are set on at each step, 

 and four times during the process one hole is set back. The 

 resulting error in the division of 127 is quite trifling ; and 

 even a considerable error in this respect has but a small influ- 

 ence on the scale. 



There is a similar approximation depending on a micro- 

 meter-wheel of 60, which any one can make for himself from 

 the ordinary divisions of the lathe-head. 



The immediate object was the division of two scales of mil- 

 limetres and fiftieths of an inch for a bifilar suspension in 

 course of construction. 



XXX. Notices respecting Neiv Books. 



The Elementary Part of a Treatise on the Dynamics of a System of 

 Rigid Bodies, being Part I. of a Treatise on the whole subject ; with 

 numerous examples. By Edward John Route:, F.R.S. Fourth. 

 Edition, revised and enlarged. (London : Macmillan, 1882. 

 Pp. xii + 385.) 

 r PHE task imposed upon the reviewer of such a work as the one be- 

 -*- fore us is easy. It has reached a fourth edition, and is written by 

 a mathematician than whom no one more competent for this special 

 branch could be found. The success o£ the work and the careful 

 examination which each successive edition has un ergoie relieve 

 the reader from the search for errors in statement of principles or 

 in solution of exercises. The outward aspect and the inward 

 arrangement are little different from those of the third edition of 

 1877. " In order to render the book less bulky for the student, 

 it has been divided into two parts. In the first volume there will 

 be found all the elements or the subject together with some methods 

 which are intended for the more advanced student. In the second 

 part the higher applications will be given." We need say little 

 under the head of arrangement of subjects, which has been carried 

 out on the lines of the last edition ; but we notice the use of heavy 

 type at the head of very many of the articles, thus bringing the sub- 

 ject to be treated of more prominently before the student : we notice 

 also in some cases an improved form of arrangement of the matter 

 of the articles. A very cursory comparison of this edition with 

 the last will show that " many additions have been made to every 

 part of the subject." 



Chapters I. to VII. treat of the same subjects in the two editions 

 (third and fourth) now before us. In Chapter III. there are four 

 additional articles devoted to the Anemometer called a " Robinson," 

 which consists of four hemispherical cups attached to four horizontal 

 arms which turn round a vertical axis ; the articles are founded 



