\\2 



NATURE 



[September 7, 191 1 



ductions. Air is supposed to be a frictionless fluid, 

 and it needs some little care to distinguish between 

 deductions from theory and experiment. With tin- 

 assumptions clearly stated the chapters would be 

 sound. 



The applications of principles and tables to designs 

 will be quite easily understood and appreciated, the 

 calculations involving only the most elementary know- 

 ledge of algebra, and the guiding principles being 

 quite trustworthy. 



Laboratory apparatus does not make an impressive 

 portion of the book, the notes given being of very 

 general interest only, and in most cases insufficient 

 to give any practical guidance to students new to 

 experimental aerodynamics. 



The remainder of the book is then occupied by 

 descriptions of the successful flying machines and 

 engines. As before, when the author was dealing 

 with established data, the work is good, and as com- 

 plete as is possible at the present time, the items of 

 further interest being difficult to obtain. 



The book is well worth reading by anyone starting 

 on a study of aeronautics, as, in spite of its simple 

 and elementary character, it is a fairly complete 

 survey of the more trustworthy existing knowledge 

 and practice. 



(2) It is exceedingly difficult to appreciate the point 

 of view of the author of this book. The mechanical 

 principles involved are curiously contorted, and a 

 brand new theory of lift is put forward which tin 

 author confesses may be defective. The theory is then 

 justified by the remark that if modified as indicated 

 " such a theory could not give any determinate 

 data." 



Many of the calculations are nevertheless right, 

 and, in fact, are usually so on the assumptions 

 adopted. 



Passing over minor points, we find on p. 17 that 

 velocity and acceleration have come to mean so 

 much the same thing to the author, that the reader 

 is told that if V be the vertical velocity of a weight 

 W, which is moved by pushing an inclined plane 

 under it, the vertical force on the plane when moving 

 with constant forward velocity is greater than the 



force when the plane is at rest by . By sacri- 

 ficing consistency, however, the author gets back to 

 better dynamical principles when dealing with fluids. 



In order to make the mass of fluid dealt with deter- 

 minate, various arbitrary and improbable assump- 

 tions are made, and considering everything, the con- 

 sequent numerical results are remarkably good. A 

 wholesome respect for records of flights enables the 

 author to extract multiplying factors to replace defects 

 of theory. 



On p. 23 is given an a priori proof that a " partial 

 vacuum cannot be produced in tin neighbourhood of 

 an aeroplane in an open atmosphere. In view oi 

 experimental evidence thai "partial" vacua are ex- 

 tremely important, an a priori proof is absolutely 

 worthless. The argument is, however, consistent with 

 a general attitude of doubt as to the value of experi- 

 ments on models, the law of relative motion, ami tin 

 NO. 2184, VOL. 87] 



resources of scientific inquiry not being fully appre- 

 ciated. (Pp. 02-3, &C) 



The very difficult problem of obtaining automatic 

 stability is dismissed in live lines as a simple problem 

 having many simple solutions. 



To anyone beginning the serious study of flight 

 this book would appear to be a dangerous intro- 

 duction. L. Bairstow. 



OUR BOOK SHELF. 

 School of Agriculture, Cambridge. A Course of 

 Practical Work in Agricultural Chemistry for Senior 

 Students. By Prof. T. B. Wood. Pp. 50. (Cam- 

 bridge: University Press, 191 1.) Price 25. 6d. net. 

 In this modest booklet Prof. Wood sets out the 

 practical exercises through which his students ate ex- 

 pected to work during their course in the Cambridge 

 School of Agriculture. It will be studied with interest 

 bv teachers of agricultural chemistry in other colleges, 

 who have not as yet any very extensive text-book 

 literature at their disposal. Further, many of them 

 will be anxious to learn as much as possible of the 

 secret of Prof. Wood's success, and to see the details 

 of the course he has evolved since he has been respons- 

 ible for the teaching of agricultural chemistry at 

 Cambridge. 



The exercises set are mainly analytical. Right 

 from the outset the student has to use the accepted 

 method, working it out in all its details ; there are no 

 short class-room methods such as would have to be 

 discarded later. Much time is thus saved, for the 

 student has nothing to unlearn when he leaves college 

 and has to attack actual problems in a technical labora- 

 tory. The system is only possible, of course, when 

 the student has already had a certain amount of ex- 

 perience of chemical work before turning to agricul- 

 tural chemistry, but this ought always to be the case. 

 Where methods are so conventional as they neces- 

 sarily are in agricultural chemistry, there is little 

 room for originality, but Prof. Wood is not entirely 

 hampered by custom, and has not hesitated to s, r ive 

 newer methods where any advantage is to be gained. 

 Thus he uses Neubauer's method for determining the 

 potash and phosphoric acid in soils, which for some 

 reason or other is not commonly used in England in 

 spite of its accuracy and rapidity. He also describes 

 the volumetric method of determining phosphoric acid, 

 in addition to the ordinary gravimetric method. 

 Other exercises include short studies of clay, sand, 

 and humus, the retention of manures by soil, and 

 experiments on oils and proteins. Sufficient detail is 

 everywhere s^iven to enable the student to work on 

 his own account, but there is nothing superfluous, and 

 the whole forty sections go into fifty pages. Alto- 

 gether the book can be cordially recommended for 

 advanced students, and also for the growing class of 

 men who have to carry out agricultural examinations 

 and analyses but do not want to purchase the large! 

 costlv manuals. Most of the routine work of an 

 agricultural laboratory is described. !•".. J. R. 



Physical Geography for Schools. By B. Smith. Pp. 



viii • [London: A. and C. Black, 1911.) Price 



35. 6d. 

 "We have,'* wrote- YV. D. Cooley in 1S75, "numerous 

 treatises on physical geographj which are in reality 

 merebj outlines of geology," and he attributed them 

 to the influence of the ardent geologists of half a 



I century earlier who had ennobled the rudiments of 

 geography connected with their own pursuits with the 



! title of physical geography. 



