January 20, 19 16] 



NATURE 



563 



<lynamical principles. Chapters ix.-xii. deal with 

 stresses and strains in joints, frames, and 

 _g'irders; chaps, xiii.-xv. with centres of gravity, 

 friction, and curved paths ; and the last with 

 mechanisms. 



(2) This introduction to the study of fluids is 

 intended '* for candidates for entrance scholarships 

 and other examinations, for naval and military pre- 

 paration, for those technical students takin?^ the 

 Board of Education lower examination in theo- 

 Tetical mechanics (fluids), or any of a similar 

 -character held by the various provincial educa- 

 tional unions." For these purposes it would seem 

 u, be an adequate and sound presentation of the 

 M'.l)ject. In addition, it will also serve to give 

 tlic student a sound knowledg^e of the subject— a 

 result almost as important. Part i., on the me- 

 chanical basis of the subject, mig^ht possibly have 

 licen omitted with advantage as the majority of 

 •students would come to the study of fluids with 

 a preliminary knowledge of dynamics from other 

 >ources. The succeeding parts deal with liquids 

 at rest, in motion, properties of gases, and 

 finally with applications. This last contains a 

 \aluable addition to the usual list of old friends, 

 and deals with a number of recent inventions of 

 special interest as illustrating principles. The 

 book affords an excellent example of the combina- 

 tion of logical development and exactness of ideas 

 with the stimulating effect aroused by dealing 

 with real problems. 



(3) The scope of this book is best shown by 

 the following extracts from the preface. "This 

 book is intended as a text-book for use in con- 

 nection with a course of experimental lectures." 

 "The aim of the writer should be to present funda- 

 mental principles clearly and accurately." "I 

 hav^e endeavoured to leave out everything- not of 

 fundamental importance." "The kind of text- 

 book which contains a little about everythin.;^;- does 

 more harm than good." It is thus seen how 

 much the intention of the author differs from that 

 ot the g^enerality of writers of text-books for first 

 year and elementary students. The result is a 

 very clear and excellent introduction to the sub- 

 ject of mechanics, properties of matter, heat, 

 '^ound, and light, suitable to the needs of uni- 

 \ crsity students in their first year and taking 



ricula for pure science, medicine, or applied 

 < nee. It is a book for which examinations 

 should be suitable, laying sound foundations for 

 future developments in greater or less degree as 

 may be required for the more specialised curricula 

 ul the second and third years. Where an effort 

 has been made to circumscribe the field, differences 

 of opinion may arise as to whether it may not 

 have been carried too far, but each individual 

 NO. 2412. VOL. 96] 



teacher can always remedy this in the case of his 

 own stydents. For example, it may be doubtful 

 if it is desirable to leave out all consideration of 

 radiation or whether more application of prin- 

 ciples to explain common and everyday experiences 

 might not have been given with advantage — in 

 spite of the fact that to the author such things 

 may be hackneyed. 



No sets of examples for exercise are given. 

 This is a disadvantage for private students. Any 

 competent teacher giving a course of experimental 

 lectures will have his own selection. To such the 

 book can be confidently recommended. It has 

 the good paper, printing, and clearness expected 

 from the Pitt Press. It is curious to see in a 

 book printed inilin English University a statement 

 that thermometers may be standardised by send- 

 ing them to the Bureau of Standards at Wash- 

 ington, U.S.A., or similar institutions in other 

 countries. In another edition the explanation of 

 the total reflection of the ordinary ray in a Nicol's 

 prism should be amended. Also the melting-point 

 of sodium thiosulphate ("hypo") is not 9*9° C. 



OUR BOOKSHELF. 

 A Coxirse in Invertebrate Zoology. A Guide to 

 the Dissection and Comparative Study of In- 

 vertebrate Animals. By Prof. H. S. Pratt. 

 Revised edition. Pp. xii+228. (Boston and 

 London: Ginn and Co., 191 5.) Price 65. 

 This book is intended as a guide to the study 

 of each of the. larger groups of invertebrates. 

 About forty animals are considered in the space 

 of 196 pages, consequently the descriptions of 

 many of them — clear so far as they go, and 

 accurate, the lapses being few and of little 

 moment — ^are brief, though several, e.g. the squid, 

 are more fully treated. The chapters deal respec- 

 tively with the arthropoda, annelida, flat worms, 

 polyzoa, mollusca, tunicates, echinoderms, 

 Cnidaria, sponges, and protozoa. The revised 

 edition contains instructions for the examination 

 of six types not included in the first edition, 

 namely, a fly, spider, oyster, sea-cucumber, 

 Gonionemus, and a sea-anemone. In the account 

 of the fly attention is directed to the " antennae, 

 with their pinnate terminal portion " (the portion 

 referred to — the arista — is, however, not terminal 

 but dorsal), but the palps are not mentioned, and 

 no attempt is made to elucidate the structure of 

 the proboscis. 



In the classification given in the appendix the 

 sponges are classed with the Cnidaria as coelen- 

 terates — implying a relationship which modern 

 work has shown to be untenable ; another obsolete 

 feature is the retention of the "phylum" Vermes 

 to include a heterogeneous assemblage of animals 

 — flat and round worms, rotifers, polyzoa, brachio- 

 pods, Phoronis, Chaetognatha and Siounculoidea 

 (the annelids are placed in a separate phylum). 



