APPLIED MATHEMATICS 527 



out this object he remembers that one must not expect too much 

 mathematical knowledge of men engaged in what is a practical 

 art based on technological science. The book thus makes 

 easy reading. 



Having set out the theory of the subject, with special re- 

 ference to performance in the air, including cruising for long 

 distances, on the ground and on the water (for a hydroplane), 

 the author gives the exact procedure of carrying out these cal- 

 culations in practice, and finally he shows the processes as 

 actually applied to a definite machine. 



The most interesting point in the theoretical portion is the 

 author's introduction of the parameter X which represents the 

 ratio of the lift coefficient to the maximum value of the same 

 coefficient. He is thus enabled to tabulate graphically the 

 necessary corrections for aspect ratio, gap chord, stagger, dimen- 

 sions, etc., in a very simple manner. 



Recent papers also include the following : 



Taylor, G. I., Scientific Methods in Aeronautics, Aer. Jotir., xxv, 1921, 474- 



91. 

 Glazebrook, R. T., Some Points of Importance in the Work of the Advisory 



Committee for Aeronautics, ibid., xxiv, 1920, 479-95. 

 Richard, P. and M., Sur le probldme general de I'aviation, Comptes Rendus, 



173, 1 92 1, 758-60. 

 Brodetsky, S., Aeroplane Mathematics, Math. Gaz.. x, 1921, 257-81, giving 



performance calculations in a very simplified form. 

 Hill, R. M., The Manoeuvres of Getting Off and Landing, Aer. Jour., xxv, 



1921, 510-36, 665-71. 

 HuNSAKER, J. C, Naval Architecture in Aeronautics, ibid., xxiv, 1920, 321- 



405. 



ASTRONOMY. By H. Spencer Jones, M.A., B.Sc, Chief Assistant, 

 Royal Observatory, Greenwich. 



The Scale of the Universe. Bulletin No. 1 1 of the National 

 Research Council of the National Academy of Sciences, Wash- 

 ington, contains two articles of great interest dealing with this 

 subject by Harlow Shapley, formerly of the Mount Wilson 

 Observatory and recently appointed Director of the Harvard 

 Observatory, and Heber D. Curtis, Director of the Allegheny 

 Observatory, respectively. These two writers are protagonists 

 of two opposite views as to the scale of our Galactic System. 

 Dependent upon the view taken as to the scale of this system 

 is the further question as to whether the spiral nebulae are 

 " island universes " in space or are common members of one 

 large system. 



One of the main points upon which the discussion turns is 

 the order of distance to be assigned to globular clusters. It is 

 assumed that these belong to the Galactic System ; their marked 



