July 8, 1922] 



NATURE 



35 



trate their applications in connexion with important 

 practical problems. To determine the flow in pipes 

 and channels the author adheres to the old Chezy 

 formula and gives tables of values of the coefficient C. 

 He not unreasonably points out that this formula has 

 the advantage of simplicity over the logarithmic 

 formulae, but he does not adduce evidence from his 

 experience as to the comparative accuracy of the results 

 they give. Thus the serious student of hydraulics can 

 scarcely be satisfied with the treatment. 



The chapter dealing with variable flow in open 

 channels is of considerable interest and importance, 

 and contains valuable suggestions to those who deal 

 with such channels, especially when the streams are 

 dammed by weirs and barrages. The correct form of 

 the surface up stream from such barrages is, however, 

 not satisfactorily discussed ; the problem is admittedly 

 a difficult one, but of importance, and needs more 

 adequate treatment than that given by the author. 



The brief chapter on unsteady flow deals with the 

 time of emptying vessels and with waves in open 

 channels ; there are also brief remarks on the effects 

 of waves and floods assisting in scouring or causing 

 deposits. The work concludes by a brief chapter 

 on the dynamic effect of flowing water. 



The student will find this work suitable for reading 

 in conjunction with some work on hydraulics which 

 deals with the subject from the fundamental rather 

 than from the practical engineer's point of view. The 

 development in the volume under notice is not suffi- 

 ciently logical for the student desirous of under- 

 standing thoroughly the fundamentals of the subject, 

 but he as well as the practising engineer will find it 

 both useful and interesting. F. C. L. 



Our Bookshelf. 



Applied Entomology : An Introductory Text-book of 

 Insects in their Relations to Man. By Prof. H. T. 

 Fernald. (Agricultural and Biological Publications.) 

 Pp. xiv + 386. (New York and London: McGraw- 

 Hill Book Co., Inc., 1921.) 215. net. 



Text-books of applied entomology are usually com- 

 piled according to one of two methods. In one type 

 of book the various injurious insects are classified and 

 ■enumerated under their respective orders and in the 

 other type they are dealt with under the crops or other 

 objects with which they are associated. The first 

 method, which is the one adopted by Prof. Fernald, is 

 unquestionably the better way of presenting the subject 

 to the elementary student. The alternative method is 

 more adapted to the needs of a practical reference 

 book, in which the primary consideration is to render 

 the information available by means of the most con- 

 venient, although not necessarily the most scientific, 

 manner of presentation. 



NO. 2749, VOL. I 10] 



Prof. Fernald has carried out his task with conspicu- 

 ous ability, and the book is certainly worthy of the 

 Massachusetts school of entomology. Within a com- 

 pass of less than 400 pages he manages to give the 

 essential facts concerning the biology and control of 

 all the more important insects affecting man, either 

 directly or indirectly, in the United States. The 

 general introductory chapters are perhaps a little too 

 much abbreviated ; nevertheless, they contain the 

 essential elementary facts concerning the structure and 

 metamorphoses of insects, and the principles of control 

 commonly in vogue. ' Twenty-four orders of insects 

 are recognised, and each is dealt with in turn, whether 

 it contains injurious species or not. The student is 

 thus enabled to view the class Insecta more or less as 

 a whole, and appreciate the place of each order in the 

 scheme of nature. The work is adequately illustrated 

 and well printed. A few misprints are noticeable in 

 the explanatory text relating to eight or nine of the 

 illustrations, but they are not sufficiently serious to 

 detract from the value of the book. A. D. Imms. 



Exploration of Air : Out of the World North of Nigeria. 



By A. Buchanan. Pp. xxiv + 258. (London: John 



Murray, 1921.) i65\ net. 

 The journey which Mr. Buchanan describes in this 

 volume was undertaken at the instance of Lord 

 Rothschild. Its object was to link up the chain of 

 zoological geography across the country lying between 

 Algeria and Nigeria. Starting from Kano in Northern 

 Nigeria, the author traversed the French Territoire 

 Militaire du Niger of the Western Sudan and reached 

 the mountainous region of Air, which had not been 

 visited by any European since Dr. Barth passed 

 through it seventy years ago. Mr. Buchanan's style 

 is vivid and his narrative racy ; he touches but lightly 

 on the hardships he had to endure in this arid section 

 of the African continent. He is at his best when he 

 describes the vicissitudes of tracking down some much 

 coveted specimen. His accounts of the natives with 

 whom he came into contact, although not sufficiently 

 detailed to be of much value to the ethnologist, will 

 give the general reader a very good idea of the character 

 of these peoples. He devotes a chapter to the Touaregs 

 of Air, in which he gives a very fair account of the 

 more salient elements of their culture and of their 

 costume, of which the veil worn by the men is the 

 most characteristic feature. It is to be regretted, 

 however, that he has not given a more detailed de- 

 scription of a people so little known. 



The Principles of Radiography. By Dr. J. A. Crowther. 



Pp. vii+138. (London : J. and A. Churchill, 1922.) 



is. 6d. net. 

 Dr. Crowther's book is intended primarily for those 

 beginning the study and practice of medical radiology, 

 to whom it should be of considerable service. The 

 author gives in a lucid and practical manner an 

 account of the principles involved in the production 

 of a skiagram and the mode of construction and action 

 of the apparatus used. The subject-matter of the 

 book forms part of a series of lectures given by the 

 author to candidates for the Diploma in Medical 

 Radiology and Electrology at Cambridge University. 



