MOTION OF THE GAS SPHERE 



281 



These and other data are fitted by a straight hne of slope — 5/6 except 

 for depths less than 200 feet, the points for shallower charges showing 

 periods increasingly less than the predicted values. This difference is 

 to be expected when the depth is not more than a few times the maxi- 

 mum bubble radius, and the results of more detailed investigations of 

 the effect are discussed in section 8.9. 



The variation of period in proportion to the cube-root of charge 

 weight has not been directly verified over nearly the range as for the 



700 

 600 



500 



400 



o 



LJ 



</> 300 



o 

 o 

 a: 



o! 200 



100 



O 



100 200 300 400 500 600 



DEPTH (ft) -^ 33 FT. 



Fig. 8.5 Bubble periods against depth for 0.55 pound tetryl charges. 



800 



variation Avith depth, but there is no reason to doubt the correctness of 

 the predicted law. For example, 25 and 300 gram loose tetryl charges 

 fired at a depth of 12 feet in 24 feet of Avater gave values of the constant 

 K in Eq. (8.11) differing by less than 1 per cent. The effects of the 

 surface and bottom on period, discussed in sections 8.8 and 8.9, are not 

 given exactly by theoretical corrections which have been developed, but 

 except for this small uncertainty it appears that the bubble periods for 

 }/2 pound and 300 pound TNT charges require constants K in Eq. 



