MOTION OF THE GAS SPHERE 



351 



the surface repulsion observed is in rather good agreement with theory, 

 and that for charges of 1 pound or less the predicted attraction of the 

 bottom is fairly well confirmed. The data of the Willis' for migrations 

 and periods of 5 pound charges and period data for 300 pound TNT 

 charges fail to indicate more than a fraction of the predicted bottom 

 effect, and migration results for 300 pound charges fired in 100 feet of 

 water are consistent with this conclusion. These results (105) are less 

 accurate than the values for small charges, owing to errors of ranging 

 and ambiguity of ranging reference marks on the pulses, but the ob- 



30 



40 



20 



HEIGHT OVER BOTTOM (FT) 



CHARGE DEPTH ( FT) 



Fig. 8.24 Migration of the bubble from 300 pound TNT charges fired in 100 



feet of water. 



served values plotted in Fig. 8.24 show no reproducible stabilized posi- 

 tion of zero migration at the predicted point 15 feet above the bottom. 

 The gear used in setting the 300 pound charges was suspended from 

 the surface and precise measurements of the charge-bottom distance 

 were not possible. As a result, the depths corresponding to the experi- 

 mental values may be subject to random errors, but the failure to obtain 

 consistent zero or downward migrations argues against the existence of 

 a stabilized position. Three points do indicate zero migration at about 

 the predicted position, but failure to reproduce these values makes their 

 accuracy somewhat dubious. At shallower depths between 35 and 75 

 feet, gravity is the main factor in determining the upward rise, and the 

 experimental points are seen to be in good agreement with the solid line 

 predicted by theory. The smaller migrations observed near the sur- 

 face are appreciably less than predicted by the small theoretical correc- 

 tion (dashed line), but it is believed that the differences are probably 

 attributable to systematic ranging errors of as much as 5 feet resulting 

 from the indicated sound source lying on the undersurface of the bubble. 



