RECENT ADVANCES IN SCIENCE 187 



of the abstract nature of the problem when simplified into 

 something that can be attacked by present mathematical 

 analysis, since viscosity has to be omitted in general. We 

 must wait till we learn more concerning the nature of the 

 viscous forces in simple types of motion in a gas or liquid. We 

 note that Guillet (Comptes Rendus, 166, 33-5, 191 8) has investi- 

 gated experimentally the viscosity couple in the case of a lamina 

 endowed with oscillatory rotation in its own plane. 



Lord Rayleigh {Phil. Mag. (6) 35, 1-12, 157-63, 191 8) con- 

 siders the two-dimensional problem of lubrication, theoretically 

 and experimentally. 



The question of the motion of solid particles in a viscous 

 liquid arises in connection with the separation of materials for 

 grinding and polishing glass surfaces in industrial optics. A 

 lecture entitled "Polish" delivered by Lord Rayleigh before 

 the Royal Institution in 1901 has recently been reprinted in 

 the Transactions of the Optical Society (19, 38-47, 191 7). The 

 same volume contains a contribution on the subject by J. W. 

 French — " The Grading of Carborundum for Optical Purposes " 

 (ibid. 1-37). 



Returning to aeronautical research we have the paper by 

 M. A. S. Riach (Aeron. Jour. 21, 123-41, 1917) on "The Screw 

 Propeller in Air," where the author discusses his blade element 

 theory of the air-screw, combining it with Froude's theory for 

 screws in ships and Lanchester's and Drzewiecki's investiga- 

 tions on aeroplane propellers. J. A. Bothezat, in a paper pub- 

 lished at Petrograd (August 191 7), examines the various types 

 of screw propellers, ventilators, helicopters, and turbines, sum- 

 ming them up in one composite theory. A general account of 

 the possible lines of progress in aeroplane performance is given 

 by F. M. Green (Aeron. Jour. 22, 3-16, 191 8), whilst the 

 interesting paper by R. Mullineux Walmsley and C. E. Larard 

 on " The Training of Aeronautical Engineers " (Aeron. Jour. 

 21, 403-19, discussion 430-38, 191 7) contains much that teachers 

 of applied mathematics may read with profit. 



Other papers on applied mathematics published in the last 

 few months are as follows : 



Statics. — Mesnager (Comptes Rendus, 165, 55 1-3, 997-1000, 

 iio 3 - 5> I 9 I 7) continues his work on the bending of beams and 

 plates. 



J. W. Nicholson (Proc. Roy. Soc. 93, A, 506-19, 191 7) calcu- 



