Waves generated by Impact. Ill 



different materials. On trying the effect of a pair of wooden 

 balls and those of a pair of billiard balls of equal size, the 

 latter were found to give a deflexion about twice the 

 deflexion due to the former. In this we may trace the effect 

 not only of the larger coefficient of restitution of the billiard 

 balls, but also probably of the shorter duration of impact 

 which would be more effective in setting up an impulsive 

 wave-motion in the fluid. 



5. Summary and Conclusion. 



The intensity of the sound generated by the collision of 

 two solid spheres varies very greatly in different directions 

 relative to the line of impact, and the character of the sound 

 shows a similar pronounced variation. This observation was 

 first made with the unaided ear and communicated to me by 

 Prof. C. V. Raman, and the present work was undertaken at 

 his suggestion to investigate this effect in detail, both theore- 

 tically and experimentally. A new type of apparatus in which 

 the ballistic principle is utilized has been used to investigate 

 the intensity of the sound in different directions. The results 

 show a maximum intensity in the line of collision, practically 

 zero intensity on the surface of the cone of semi-vertical 

 angle 67°, and a second, but feeble maximum in the plane 

 perpendicular to the line of impact. These results combined 

 with the indications of theory and further observations on 

 the character of the sound-wave show that, practically 

 speaking, it is produced entirely by the accelerated motion 

 of the spheres during the impact. The law of variation of 

 the intensity of the sound with the velocity of impact and 

 the radius of the balls has also been found and tested 

 experimentally. The investigation was carried out in the 

 Laboratory of the Indian Association for the Cultivation 

 of Science. The writer hopes later on to carry out further 

 work on the subject, particularly in the matter of getting 

 direct records of the character of the sound-wave and ob- 

 serving the effects of oblique impact and the impact of spheres 



of unequal diameters. 



Calcutta, 

 28th January, 1916. 



m 



! 



