390 



NATURE 



[May 26, 1921 



plane, and should make a good preliminary text- 

 book for a degree in aeronautics. 



(2) In his preface Mr. Park says that his aim 

 has been tp consider problems of airscrew design 

 and construction from the point of view of the 

 designer. In so doing he explains methods de- 

 veloped for the Lang Propeller Co., Ltd. A very 

 considerable degree of success has been attained, 

 and the book is not difficult to follow. The items 

 of calculation are given in great detail, but are 

 connected with the main outlines of airscrew 

 theory so closely that the book may be used by 

 later workers even when they are more up-to-date 

 in their theories. 



It is very noticeable that the two latest books 

 dealing with the subject of airscrew design adopt 

 the attitude that the oldest theory agrees better 

 with practice than a new and presumably sounder 

 one. Empiricism has to this extent rather re- 

 tarded the development o£ the subject. The 

 theory adopted in the early days of aeronautics 

 ignored the influence of previous passages of the 

 airscrew blade and its companions, and the effect 

 was found in a disagreement between prediction 

 and observation. An examination of the theory 

 by Lanchester, De Bothezat, and others indicated 

 a loss of efficiency and of torque which was great 

 for the stationary airscrew or helicopter, and of 

 less importance at the highest speeds of flight of 

 an aeroplane. The most difficult part of design 

 being the production of an airscrew which allows 

 the engine to develop full power at a given speed, 

 it was found that the introduction of an inflow- 

 factor indicated by a modified theory was advan- 

 tageous. In the later periods of development the 

 magnitude of the inflow factor required has been 

 found to decriease to the point at which it may be 

 ignored. It is highly probable that this is an 

 incorrect view of the phenomena, and that it 

 would be much more sound to attribute the 

 change to an opposing change due to the com- 

 pressibility of the air. The importance of this 

 latter factor depends on the tip speed of the air- 

 screw, a quantity which has been steadily increas- 

 ing. No one has yet propounded a working 

 theory which is based on the best established 

 theoretical data. 



The greater part of the treatise by Mr. Park 

 is independent of the refinements mentioned above, 

 and gives a good analysis of the possibilities of 

 airscrew design. In commending the book to 

 readers, one may suggest that it will cover the im- 

 mediate needs both of a designer and of a scien- 

 tific student of sufficient ability. A thesis of con- 

 siderable value might be produced as a result of 

 the data of the book and the critical faculties of 

 the student. 



NO. 2691, VOL. 107] 



Our Bookshelf. 



Practical Biological Chemistry. By Prof. G. 

 Bertrand and P. Thomas. Translated from the 

 third edition by Hector A. Colwell. 

 Pp. xxxii-f348. (London: G. Bell and Sons, 

 Ltd., 1920.) I05. 6d. net. 



This work will be found of great value by 

 students and, perhaps more particularly, by 

 teachers of biochemistry. The object of the 

 authors has evidently been to provide a series of 

 laboratory exercises illustrating the properties of 

 the chief substances of biochemical interest, and 

 at the same time affording examples of the 

 methods used in the various branches of bio- 

 chemical investigation. A large number of tests, 

 interesting preparations and estimations are de- 

 scribed in the first part (Statics), whilst in the 

 second part (Dynamics) the subjects of en- 

 zymes, micro-biology, and fermentations are 

 treated experimentally. 



Although the whole range of biochemistry is 

 dealt with, and the exercises are chosen quite 

 impartially from the chemistry of animal and 

 vegetable life, the treatment is nevertheless very 

 unequal as regards both the selection of methods 

 and the degree of detail given. For example, as 

 all readers would desire, a very full account of the 

 admirable Bertrand method for the estimation of 

 sugars is given, and, similarly, Duclaux's ingeni- 

 ous distillation method for the estimation of vola- 

 tile acids is fully described. On the other hand, 

 although several pages are devoted to the amino- 

 acids, and Sorensen's formaldehyde titration 

 method is described, there is no mention of van 

 Slyke's method for the estimation of amino- 

 nitrogen, and, indeed, the name of van Slyke does 

 not occur in the index. Again, the conception of 

 hvdrogen-ion concentration is mentioned, but na 

 practical use of it is made in the book. It is on 

 account of this arbitrary element in the treatment 

 that we consider the book as likely to be of 

 greater value for teachers than for students ; but 

 whoever uses it will find in it many interesting and 

 unusual experiments, described in a clear and 

 suggestive manner, without too great a load of 

 detail. The translator has done his work well, and 

 has added a few notes, including a detailed 

 description of the use of the Maquenne block 

 for the determination of melting points. 



A. Harden. 



Wireless Telegraphy: With Special Reference to 

 the Quenched- Spark System. By B. Leggett. 

 (The Directly-Useful Technical Series.) 

 Pp. XV -f 485. (London: Chapman and Hall,. 

 Ltd., 192 1.) 305. net. 

 We welcome this volume, which gives full prac- 

 tical details of the " Telefunken " or quenched- 

 spark system of radiotelegraphy. (We use this 

 word, for we think it will shortly receive inter- 

 national sanction.) Practically all the treatises, 

 on this'subject published in English concern them- 

 selves mainly with the Marconi system, and dis- 



