278 



MOTION OF THE GAS SPHERE 



taken by Edgerton of detonator caps exploded at various depths. Ex- 

 perimental points measured by Ewing and Crary (32) from one such 

 record are plotted in Fig. 8.2,^ and the solid curve is taken from Her- 

 ring's calculations based on Eq. (8.7), the value of a^ having been chosen 

 to give agreement with the experimental observations. It is seen that 

 the simple theory predicts a curve of the same general form but some- 

 what broader than that found experimentally. The most likely expla- 

 nations of the difference appear to be either that optical distortions in the 

 experimental arrangement caused errors or that the proximity of the 



20 



10 



20 



60 



40 



TIME (msec ) 

 Fig. 8.3 Radius-time curves for small tetryl charges. 



80 



free surface twelve inches above the charge and a steel plate beneath it 

 had significant effects. 



These early photographs of Edgerton showed that the bubble rose 

 slightly during its first expansion and then sank rapidly several inches 

 below its initial position. This repulsive effect of the free water sur- 

 face and a similar attraction toward a rigid surface has been further 

 investigated by a number of workers, notably by Campbell and Wyckoff 

 (17, 18) at the Taylor Model Basin and by Taylor and Davies (109) in 

 England. Herring was the first to develop the hydrodynamic theory 

 of these effects, which are discussed in more detail in section 8.8. 



A considerable number of measurements of bubble radius-time 

 curves for various small charges and depths of explosion have been 

 made at the Woods Hole laboratory.^ These data have been obtained 



* The data for Fig. 8.2 are taken from Herring's report (46) . 



3 These experiments, carried out in cooperation with personnel at the Taylor 

 Model Basin (U. S. Navy), are described in a r(>i)()rt by Arons, Borden, and 

 Stiller (2). 



