96 Mr. Sudhansukumar Banerji on Aerial 



6. The " metamict " crystal o£ thorite gave no X-ray 

 reflexion. The lattice is completely destroyed. 



7. Experiments on the intensities of the normal spectrum 

 have shown that different faces of the same crystal give a 

 different law of the variation of intensities with increasing 

 order. 



I have much pleasure in thanking Professor W. C. Brogger 

 for lending me, from the excellent collection of his laboratory, 

 the crystals necessary for this research, as also for the kind 

 interest he has taken in the work. 



I am also very much pleased to thank Mr. H. Schjelderup 

 for his most valuable assistance in making the observations 

 on which the present work is based. 



Physical Institute, Cliristiauia. 

 March 31, 1916. 



VII. On Aerial Waves generated by Impact. By Sudhan- 

 sukumar Banerji, Al.Sc, Sir Rashbehari Ghosh Research 

 Scholar in the University of Calcutta* . 



1. Introduction. 



HERTZ, in his well-known paperf on the collision of 

 elastic solids, shows that when two bodies impinge 

 on each other with moderate velocities, the elastic distortions 

 are more or less entirely localized over the region of contact, 

 and that the duration of impact, though in itself a very 

 small quantity, is a large multiple of the gravest period of 

 free vibrations of either body. It follows, therefore, that 

 no appreciable vibrations of the solids are set up by the 

 impact, and that all parts of the impinging bodies, except 

 those infinitely close to the point of impact, move as parts 

 of rigid bodies. 



In a recent paper % Lord Rayleigh has investigated the 

 circumstances of the first appearance of sensible vibrations 

 in the case of two impinging spheres, and his results seem 

 to show that if vibrations are excited at all, the leading term 

 in the radial displacement at the point of contact during the 



* Cornniunicated by Prof. 0. V. Raman, M.A. 



t Hertz's ' Miscellaneous Papers/ English Edition, p. 146. [See also 

 Love's ' Treatise on Elasticity,' Second Edition, p. 195.] 



X Lord Rayleigh, " On the Production of Vibrations by Forces of 

 Relatively Long Duration with Application to the Theory of Collisions," 

 Phil. Mag. vol. xi. pp. 283-291 (1906). ['Scientific Papers,' vol. v. 

 pp. 292-299.] 



