APPLIED MATHEMATICS 525 



J. Andrade, ibid., 171* 1920, 664, who examines the case where 

 the friction is proportional to the displacement, and by R. 

 Serville, ibid., 173, 1921, 404-7, 470-2. 



The study of aeronautics is proceeding apace. The first 

 question that engages the attention of researchers is that of air- 

 resistance. Theoretical methods are at present insufficient 

 for practical needs, and aviation is based principally on experi- 

 mental researches. A valuable paper is that by J. R. Pannell 

 on " Fluid Resistance on Bodies of Approximately Stream- 

 line Form," Aer. Jour., xxiv, 1920, 498-504. There is also a 

 paper on the laws of fluid-resistance by E. Jouguet, Comptes 

 Rendus, 171, 1920, 96-9, while on resistance in viscous fluids 

 there are papers by D. Riabouchinski, ibid., 173, 192 1, 967-9, 

 and by C. Wisselsberger. Experimental methods are discussed 

 by W. Margoulis, Comptes Rendus, 171, 1920, 997-9, and by 

 J. Villey, ibid., 172, 1921, 270-2. 



Aeroplane wings and surfaces have been the subject of much 

 discussion, principally the Handley-Page wing, which is in the 

 form of a slotted aerofoil, Aer. Jour, xxv, 1921, 263-89. Much 

 is claimed for this new type of wing, and its introduction will 

 no doubt give rise to further research on this most important 

 subject. There is also a paper by H. B. Irving on " The Design 

 of Aeroplane Control Surfaces, with Special Reference to 

 Balancing," t^tW., 537-55. 



Next comes the propeller, an ever-fruitful source of investiga- 

 tion. G. de Bothezat, whose work has already been mentioned 

 (see Sci. Prog., 192 i, 526) contributes a short paper on the 

 fundamentals of the theory of blade-screws, Aer. Jour., xxiv, 



1920, 595-600, while notes on the subject are given by M. A. S. 

 Riach, ibid., 20-4, and H. C. Watts, ibid., 406-12, both well- 

 known workers on the theory of screw propellers. 



The design of spars is the subject of papers by H. Booth, 

 ibid., xxiv, 1920, 563-74, and by H. P. Hudson, ibid., xxv, 



1 92 1, 556-8. Miss Hudson also discusses the important ques- 

 tion of " Incidence Wires," ibid., xxiv, 1920, 505-16. 



Helicopters are now a prominent subject of research, chiefly 

 experimental ; the heliocopter, however, also offers scope for 

 mathematical treatment, A useful account of the state of the 

 subject is given by L. Damblanc, ibid., xxv, 1921, 3-19, and 

 experimental flights are described by H. Pescara, Comptes 

 Rendus, 172, 192 1, 845-7, by P. Painlev6, ibid., 847-8, and 

 by E. Oehmichen, ibid., 366-8. H. Chatley writes a paper 

 on " The Problem of Flapping Flight," Aer. Jour., xxv, 1921, 

 492-503, a subject in which he has been interested for many 

 years. An account of rigid airships is given by J. L. Bartlett, 

 ibid., ZS7-77' 



The flight of birds is naturally a matter of interest to all who 



