592 



NATURE 



[January 6, 1921 



males, fighting with any intruder for all he is 

 worth. With the physiological change (partly 

 due to specific internal secretions contributed to 

 the blood-stream) there is a complete psychical 

 change in the dispositional attuncment of the 

 bird's nature. Substantially the same presentation 

 afforded by another male is now linked with quite 

 different modes of overt behaviour. No longer 

 gregarious, he is a solitary occupant of a restricted 

 domain, driving all other males away. Presently 

 he is joined by a mate, and the normal routine 

 of reproduction runs its course. But if a cold 

 snap should come on, the separated males may 

 reunite in a flock, and the male is then no longer 

 intolerant of other males. The physiological state 

 probably reverts to its winter poiSe, and with this 

 is correlated a reversion to the previous psychical 

 disposition. But it seems that when a male bird 

 (lapwing or other) has secured a territory and is 

 intolerant therein of all others save a mate, he 

 sometimes returns for a while to the flock which 

 occupies a neutral area. There he is no longer 

 intolerant of others, but moves among them on 

 quite friendly terms. Hence in different cir- 

 cumstances, (i) in his territory and (2) in the 

 flock, his disposition is different, so that occu- 

 pancy of a territory appears to be a determining 

 condition of the behaviour observed therein. If 

 this sort of thing occurred in so marked a form 

 in human life, it would perhaps be attributed to 

 "dissociation," and described as an instance 

 of double personality, two "streams of con- 

 sciousness " being separated as if by a barrier. 

 In any case, just thus, it seems, does the male 

 bird in his first year behave, though he has never 

 so behaved before, or seen others so behave. 



Exigencies of space preclude more than an out- 

 line sketch of Mr. Howard's main thesis. The 

 treatment in detail is admirable in its method of 

 raising and meeting difficulties with no attempt 

 to shirk them. The way in which the expression 

 of song may produce a different impression on 

 others at different times and in different cir- 

 cumstances is dealt with suggestively. All may 

 not agree with Mr. Howard's conclusions; but all 

 will admit the transparent candour of a genuine 

 seeker after truth. One would like to comment 

 on his contribution to the solution of the difficult 

 problem of migration — turning upon the alter- 

 nating interplay between the territorial and the 

 gregarious poise in disposition. But lack of space 

 forbids. The book is well written, well printed, 

 and well illustrated, with photogravures from 

 drawings by Mr. G. E. Lodge and Mr. H. 

 Gronwold. 



C. Ll. M. 

 NO. 2671, VOL. 106] 



Airscrews in Design and Performance 



Airscre-ws in Theory and Experiment. By A. 

 Fage. Pp. ix-l- 198+7 folding plates. (London : 

 Constable and Co., Ltd., 1920.) Price 345. 



IT is difficult to place this book in the scheme 

 of aeronautical progress, for it does not deal 

 adequately with either the theory or the practice 

 of airscrew design. The author has not succeeded 

 in the idea expressed in the first sentence of his 

 preface, where he says that "an endeavour has 

 been made to present in this work an accurate 

 and comprehensive account of the science of the 

 airscrew from both its theoretical and experimental 

 aspects." It is well known to all those connected 

 with the experimental side of aeronautics that Mr. 

 Fage, as a result of his position at the National 

 Physical Laboratory, has had greater facilities for 

 original work than any other British worker. The 

 number of papers in his name which occur in the 

 bibliography testifies to his activities, and the 

 book cannot fail to have an importance in many 

 directions. One would select chaps, v., vi., and 

 vii. — that is, those dealing with experimental data 

 — as justifying the writing of this book. 



What is missed is the presentation of the results 

 of research in a form which stimulates application 

 to the workaday theories of the immediate future. 

 Instead, one finds a very important recent develop- 

 ment of theory compressed into one and a half 

 pages of the book in such a way that, without prior 

 knowledge, it conveys nothing to the reader. The 

 basic theorem on which design rests comes from 

 the conception that the several elements of an air- 

 screw blade produce an airflow which is essentially 

 of the same character as the flow round a wing. 

 The application of this theory to aerial propellers 

 is due to Drzewiecki and Lanchester, but after 

 some little use and comparison with experiment 

 it was found to be insufficiently accurate for design 

 purposes. The necessary idea for a next approxi- 

 mation was obtained from a realisation of the fact 

 that a wing is always moving into fresh air, whilst 

 an airscrew blade moves into air disturbed by other 

 blades and by the previous passages of the blade 

 itself. The thrust of an airscrew, being produced 

 by dynamic means, involves the throwing back of 

 a mass of air per second the axial momentum of 

 which is equal. to the thrust. Owing to the con- 

 tinuity of the airflow, it might therefore be ex- 

 pected that disturbances due to other blade pas- 

 sages would take the form of an " inflow " of air 

 into the airscrew blade. Experiment provides 

 support for, and can be used to give quantitative 

 values to, a theory based on this idea. 



In discussions of marine propellers, Froude 



