597 



compute q on the basis of the existing theory provided one has a knowledge 

 of the physical properties of the gas in the bubble. Using this value of q, 

 one can compars the predicted radius-tine curve with the known experimental 

 radius-time curve as a check ori theory. In this connection it should be 

 mentioned that the experimental data probably provide an upper limit to q, 

 since the bubble is obscured at the time of the minimum by a mass of material 

 which is more likely solid than gaseous. This difficulty has been discussed 

 in detail in Sec. 8 of the present report. The other line of attack would 

 bo to use the value of q necessary to give a good fit with experimental radius- 

 time curves as an aid in arriving at suitable values for the average physical 

 properties of the gas in the bubble. 



Another of the uses to which the empirical radius-time curve has been 

 put is the following: Using the bubble theories mentioned previously, one 

 can compute the radius of the bubble for the case of a zero excess pressure 

 field surrovmding the bubble. Expressing this radius as a fraction of the 

 maximvun radius of the bubble, one can determine, from the empirical radius- 

 time curve, the fraction of the periodic time at which the excess pressure 

 vanishes. It is found that this time agrees excellently with similar times 

 determined from piezoelectric gauge measurements of the pressure field 

 surrounding the bubble 26). 



Due to the paucity of photographic data for charges fired at small 

 non-dimensional depths, no attempt has been made to develop an empirical 

 representation of the radius -time curve for this very important case. 

 However, it can be stated with assurance that Sq. (1-5) does not hold when 

 the presence of free or rigid surfaces becomes important. 



-a- 



