587 



In the shots at small values of a. the greater depressions recorded 

 by gauges 5 ajid 8 can be attributed to the proximity of each of these 

 gauges to one of the charges. In the 72° and 80° shots the lower damage 

 of gauge 17 may possibly mean that the narrow Mach region missed the 

 gauge. 



A graphical representation of the magnitude of this effect, Figxire 29, 

 shows the ratio of the maximum depressions recorded by gauges 6 and 17 to 

 the depression produced by a 22h gm. charge at it-9-l/2 in. Note that 

 gauges 6 and 17 were kS-l/2 in. from a point midway between the separate 

 112 gm. charges and hence at distances greater than '+9-1/2 in. from the 

 individual chaxges. The maximum effect was h'J'^. 



Fig. 29 



Mach effect 

 on damage. 



(c) Screening one charge by the gas bubble from another . In the 

 experiments reported in the previous section, gauges 5 and 6 were appar- 

 ently affected only by the nearer of the two charges until the distance 

 between charges was made less than 17-1/2 in. This result can be ex- 

 plained by the shielding effect of the bubble of the nearer charge on 

 the wave from the farther charge. In Figure 30 a plot is made, as a 

 fimction of the distance "b", of the average damage recorded by gauges 

 5 and 8, corrected from distance "b" to a charge -to -gauge distajice of 

 14-9-1/2 in. (a distance exponent of 1.20 was assumed.) From the damage 

 obtained for the 22k gm. charge in the center of the ring, and assuming 

 a weight exponent of 0.59, the damage to be expected from a 112 gm. 

 charge at 49-1/2 in. is O.158, which is to be compared with O.I7, the 

 average damage along the flat portion of the curve of Figure 30- It 

 might be expected that the screening effect woiild persist until the 

 charges were placed so close to one another that the gas bubbles 

 coalesced before the effective portion of the shock wave was fully 

 emitted. Table XXIV lists the data. 



