338 SCIENCE PROGRESS 



of increasing importance, both from the practical point of view and from the 

 standpoint of the teacher and student of mechanics. There is no part of 

 dynamical theory that does not enter into the discussion of aeroplane motion, 

 and, although a full treatment of the subject is bound to be very difficult, it is 

 yet possible to present it in such a way as to appeal to such as have only 

 mastered the elements of applied mathematics. Professor Williams' aim 

 is to provide an elementary account, based mainly on the course of lectures 

 delivered by Professor Marchis in Paris in 1919. The dynamical problem 

 of the aeroplane is set forth in detail. After an introductory chapter on the 

 aerodynamics of the plane and of the cambered surface, there are special 

 chapters on straight horizontal flight, descent and ascent, circular flight 

 (including circular or helical descent), performance from the point of view of 

 ceiling and radius of action, and stability and controllability, including the 

 effects of gusts of wind. There is also a brief discussion of the propeller. 

 The book thus gives a considerable amount of matter that is not to be found 

 :set out conveniently elsewhere : the treatment is on the whole clear and 

 interesting. 



There are, however, several objectionable features in the book. The 

 notation is not consistent, and therefore confusing. Errors of a literary or 

 "typographical kind are frequent enough to be irritating. References to 

 French literature on the subject are marred by ofiences against the laws of 

 -French orthography. The writer refers several times to a well-kpo-yrn 

 English book on aeronautics, and in each case the name of one of the jd . *; 

 authors is given wrong : the name of the author of another English work is 

 spelt wrongly. Such errors do not, of course, destroy the value of the book. 

 Far more important, however, are some statements of dynamical theory 

 which one cannot commend to students of mechanics. Thus, it is not correct 

 to say that " the resultant pressure is a vector. . . . We know all there is to 

 know about it if we know its magnitude and its moment about some point." 

 In another place the author says of a rigid body : " the force determines the 

 instantaneous motion of the centre of gravity, and the couple determines 

 the rotation which the machine is momentarily undergoing " ; surely in 

 ■each case it is the acceleration that is determined. 



The subject matter of the book is iiseful and valuable. It is to be hoped 

 that, if a second edition is issued, care will be taken to eliminate mistakes of 

 the kind indicated, and to improve the treatment in the direction of presenting 

 the subject in a more unified manner. 



MISCELLANEOUS 



Principles of Human Geography. By Ellsworth Huntington and Sumner 

 W. Gushing. [Pp. xiv + 430, with 118 illustrations and maps.] 

 (New York: John Wiley & Sons; London: Chapman & Hall, 192 1. 

 Price 2 IS. net.) 



The authors of this very comprehensive study of geography state that it is 

 their purpose, in the first instance, to set forth the great principles of geo- 

 graphy in its human aspects, then to provide a text-book for students able 

 to think for themselves, and to furnish would-be teachers with a solid ground- 

 ing in the human relationships which they are eager to teach. 



The physical background of geography is more or less taken for granted, 

 and a study made in every case of man's relation to his physiographic en- 

 vironment. In turn, a careful study is made of man's relation to physical 

 environment in general, to location, land forms, bodies of water, soil and 

 minerals, climate, vegetation, and animals, and to man himself. As can be 

 imagined from such an arrangement, a certain amount of overlapping or 

 repetition is almost unavoidable, but probably not more than is advantageous 

 to the young teacher. 



On the whole, the book can be strongly recommended for the purpose for 



