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- NATURE 
465 
THURSDAY, FEBRUARY 15, 1917. 
AERONAUTICAL THEORIES. 
(1) Bases Théoriques de VAéronautique. Aéro- 
dynamique. By Prof. N. Joukowski. Pp. 
xvili+227. (Paris: Gauthier-Villars et Cie, 
1916.) Price 11 francs. 
(2) Dynamical Stability of Aeroplanes. By Jerome 
C. Hunsaker, assisted by T. H. Huff, D. W. 
Douglas, H. K. Chow, and Capt. V. E. Clark. 
Pp. 78. (Smithsonian Miscellaneous Collections, 
Ixii., 5; Hodgkins Fund.) (Washington : Smith- 
sonian Institution, 1916.) 
(3) Air Screws: an Introduction to the Aerofoil 
Theory of Screw Propulsion. By M. A. S. 
Riach. Pp, viii+128. (London: Crosby Lock- 
wood and Son, 1916.) Price 10s. 6d. net. 
(4) Aérodonétique. Par F. W. Lanchester. 
Traduit de l’anglais sur la deuxiéme édition 
par le Commandant C. Benoit. (Paris: 
Gauthier-Villars et Cie, 1916.) Pp. xvii+478. 
Price 14 francs unbound. 
(1) fo the French translation of Prof. Joukow- 
ski’s work we are indebted to Dr. S. 
Drzewiecki. In a separate preface the latter 
writer emphasises the fact that the use of the prin- 
ciples of mathematical physics did not receive 
adequate attention in the early days of artificial 
flight, and he advocates the recognition of aero- 
dynamics as a separate branch of theoretical 
science. We regret to find that whatever ex- 
trameous arguments may be and have been ad- 
duced for placing this subject on an independent 
footing, there is nothing, either in the translator’s 
eloquent introduction or in the subject-matter of 
the book, to justify the present claim. 
Dr. Drzewiecki admits the important part which 
the study of fluid motions has played in the de- 
velopment of aeronautical theories. But he fails 
to realise that the matter of which the book 
treats is hydrodynamics pure and unadulterated. 
There is nothing in it of a sufficiently distinct and 
novel character to form the nucleus of a distinct 
subject with such a name of its own as aero- 
dynamics. 
On the purely mathematical side, the treatment 
does not extend very much beyond the formula- 
tion of the equations of motion and continuity for 
perfect and viscous fluids, together with the pres- 
sure equation, and a somewhat diffuse treatment 
of the laws of vortex motion. This, together with 
considerations of a practical character, occupies 
the first five chapters. The subsequent sections 
contain accounts of some of the more recent at- 
tempts to solve the equations of motion in the 
case of cylinders and laminz resembling the sus- 
taining surfaces of an aeroplane. In this connec- 
tion prominence is given to the theories and ex- 
periments of Profs. Kutta, S. A. Tchapliguine, 
and Karman, and the Aerodynamic Laboratory at 
Moscow is described in an appendix. It must not, ° 
however, be forgotten that there are two ways of 
reconciling the existence of a pressure on a mov- 
ing lamina with the properties of a perfect fluid. 
NO. 2468, VOL. 98] 
One method is to assume that there is circulation 
of the fluid round the lamina. Thus, for example, 
a cylinder in a perfect liquid acted on by gravity 
tends to travel horizontally if there is cyclic motion 
round it. This method appears to form the basis 
of most of the work in Prof. Joukowski’s later 
chapters. On the other hand, we have the theory 
of discontinuous motion, originated by Kirchhoff, 
which has now _ been greatly elaborated in 
this country by means of the Schwartz-Christoffel 
transformation. Of this theory Prof. Joukowski’s 
treatment is practically nil. 
Up to the present time very little has been done 
in investigating the motion of solids through 
compressible fluids. It is true that compressibility 
does not greatly affect the character of the motion 
so long as the velocities are everywhere small 
compared with the velocity of sound in the same 
medium. But this condition can scarcely be re- 
garded as binding in the neighbourhood of a 
sharp-edged boundary; in fact, according to 
Boyle’s law, the pressure would simply vanish 
and would not become negative at a point at which 
the velocity was infinite. The problems treated 
by Prof. Joukowski are essentially based on the 
hypothesis of a velocity potential satisfying La- 
place’s equation of continuity, and they therefore 
belong to the subject of hydrodynamics proper. 
According to the usual convention in this country, 
experimental and practical considerations regard- 
ing the motion of fluids are classified under the 
designation of hydraulics. It is very important 
that engineering students who are proposing to 
take up aeronautical work should be equipped with 
a knowledge of the necessary hydrodynamics and 
hydraulics, and Prof. Joukowski’s lectures were 
probably admirably adapted to the students in his 
classes. But the book goes only a very little way 
towards covering the subject-matter contained in 
the English treatises on hydrodynamics of more than 
thirty years ago, with their chapters on sources, 
doublets, and images, motion in rotating cylinders 
in the form of lemniscates and cardioids, motions 
of a solid in a liquid, tides and waves, and de- 
tailed treatment of discontinuous motion in two 
dimensions. It is quite clear that the advanced 
student will find it much more helpful to turn, to 
one of these early books for a thorough grounding 
in hydrodynamics than to rely on a more super- 
ficial and fragmentary treatment of the same sub- 
ject, which is all that he will find in the present 
volume. 
(2) An examination of the paper by Messrs. 
“Hunsaker and others” suggests that in the 
scientific study of aeroplane stability America is 
far behind Great Britain. The only part of this 
paper which has any claim to novelty consists in 
the determinations of the coefficients of stability 
of two aeroplanes (the Clark and Curtiss types) 
based on experiments with models. The methods 
of experimenting were identical with those 
used in our National Physical Laboratory, of 
which the details were developed by the energies 
of Mr. L. Bairstow. 
The publication of these experimental data de- 
rives additional interest from the fact that owing 
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