186 SCIENCE PROGRESS 



tion of flight, and then introducing the effect of the shape of the 

 projectile by supposing the resistance to act in the plane of the 

 axis of symmetry and of the direction of motion, at an angle 

 with the former some constant times the inclination of the 

 latter, Prescott calculates the trajectory as well as the drift 

 and the angular deflection of the axis of the projectile. 



W. A. Dalby (Proc. Roy. Soc. 93, A, 333~47, 191 7) extends 

 his graphical method of drawing trajectories, published in 

 191 5, in which the density of the air was assumed constant. 

 This restriction is now discarded so that the graphical process 

 can be extended to high-angle fire. Numerical results are given. 



P. Frank (Phys. Zeitschr. 19, 2-4, 191 8) shows that the 

 problem of steering an airship in a variable wind so as to go 

 from one point to another in minimum time leads to an equation 

 of the same type as occurs in the propagation of light in a 

 moving medium. 



J. G. Leathern {Phil. Mag. (6) 35, 119-30, 191 8) continues 

 his work on curve factors in the conformal representation 

 of hydrodynamical problems in two dimensions (see also 

 Phil. Trans. 215, A, 439~87, 191 5, and Proc. Roy. Irish Acad. 

 33, A, 35-57, 191 6). The fact that the lifting power of an 

 aeroplane is greatly improved if the wing is not flat but 

 " cambered," so as to be slightly concave on the lower surface 

 and considerably convex on the upper surface, has long been 

 made use of in practical aeronautics. On the other hand the 

 investigation of the discontinuous stream-line motion past 

 such a wing has long defied analysis. Thus Greenhill in his 

 report on the subject to the Advisory Committee on Aeronautics 

 (Report 19), published as recently as 19 10, limits himself ex- 

 plicitly to plane barriers, or combinations of plane barriers. 

 H. Levy (Proc. Roy. Soc. 92, A, 285-304, 191 6) showed how to 

 extend the classical work of Kirchhoff and Rayleigh to curved 

 boundaries. Leathern 's method consists in discovering con- 

 formal transformations applicable to curves by extension of 

 and analogy with known cases. 



The practical problem of finding the resistance to motion 

 through a medium is, however, best solved experimentally, and 

 the work of Eiffel, Dines, Bairstow and others has been mainly 

 instrumental in supplying the information upon which the 

 successful conquest of the air has been based. The hydrody- 

 namical calculations are bound to lose in practical value because 



