Ellis 



and the accelerometer record is much the same except that over a relatively 

 long period the time integral of the acceleration must be zero. A typical record 

 is shown in Fig. 15. The sweep rate is 2 milliseconds per large division, and 

 the spike on the upper oscilloscope trace indicates when a photograph was taken 

 of the cavity under observation. 



I 



wsssbbM 



Fig. 15 - Oscilloscope record of vertical 

 acceleration of the tube in Fig. 14. The 

 grid calibration is 25 g/cm and Z msec/ 

 cm horizontally. 



Typical cavities are shown in Fig. 16. The magnification is about four 

 times, but since flat windows had not yet been installed in the tube, there was 

 an apparent flattening in the horizontal direction. The cavity at the top is ac- 

 tually quite spherical. The second and third photographs show flattening of the 

 bottom, and after collapse the vertical jet and later the vortex ring may be 

 seen. This is in accord with the observations made at Cambridge. 



In conclusion it may only be said that the quantitative aspects of the work 

 are still being performed and that it is hoped that they will be presented at 

 some later time. The generalities which have been discussed should then 

 appear in sharper perspective. 



REFERENCES 



1. Euler, L., Hist, Acad. Roy. Science et Belles Lettres, Vol. 10, No. 227, 

 1754 



2. Besant, W., "Hydrostatics and Hydrodynamics," Cambridge University 

 Press, 1859 



3. Rayleigh, "The Pressure Developed in a Liquid During the Collapse of a 

 Spherical Cavity," Philosophical Magazine 34:94 (1917) 



150 



