"94 Lord Rayleigh on the Pressure developed 



much. So the deflexion for a ray of starlight grazing the 

 sun is 



250 \ 2 



2x( 



I =3-GxlO" 6 , or 0"-74. 



185000 



Longitudinal Possibility. 



The velocity of light issuing radially from a body might on 

 this hypothesis also be affected, since it could be pulled back 

 by a maximum amount represented by the free fall from 

 infinity, i. e. by \Z(2qgR); though the longitudinal q need not 

 be the same as the transverse q concerned in deflexion. 



But this sort of action, if it can be imagined as likely to 

 occur, and even if it caused a reduction in sunlight- velocity 

 of 26 miles a second in the neighbourhood of the earth, would 

 not yield any Doppler effect ; the waves would still be received 

 at their emitted frequency. 



VIII. On the Pressure developed in a Liquid during the 

 Collapse of a Spherical Cavity. By Lord Rayleigh, 

 O.M., F.R.S* 



HEN reading 0. Reynolds's description of the sounds 

 emitted by water in a kettle as it comes to the boil, 

 •and their explanation as due to the partial or complete 

 collapse of bubbles as they rise through cooler water, I 

 proposed to myself a further consideration of the problem 

 thus presented; but I had not gone far when I learned from 

 -Sir C. Parsons that he also was interested in the same 

 question in connexion with cavitation behind screw-pro- 

 pellers, and that at his instigation Mr. 8, Cook, on the 

 basis of an investigation by Besant, had calculated the 

 pressure developed when the collapse is suddenly arrested 

 by impact against a rigid concentric obstacle. During the 

 collapse the fluid is regarded as incompressible. 



In the present note I have given a simpler derivation of 

 Besant's results, and have extended the calculation to find 

 the pressure in the interior of the fluid during the collapse. 

 It appears that before the cavity is closed these pressures 

 may rise very high in the fluid near the inner boundary. 



* Communicated by the Author. 



