1341 
"regular" collision. For F in the neighborhood of 0.174 and 
for & = 20°8 the measured value of & is 2325 Ao-sgedaten than 
O& , as the theory predicts. Figure 24, Plate III, shows a 
Mach effect. The measured angle @= 39° is beyond the range 
of "regular" values (cf. fig. 10a, where & for F= 0.174 
extr. 
4s about 26326). 
The most complete quantitative investigation 16) 
has 
been carried out experimentally at the Underwater Explosives 
Research Laboratory, Woods Hole, Mass. In general, two equal 
charges are exploded simultaneously at a variable distance apart. 
The resultant effect of the shock-waves is registered by a 
piezo-electric or diaphragm gauge at some point equidistant 
from the two charges (it is convenient for this distance to be 
kept constant). Figure 25, Plate IV shows a "regular" collision 
produced by the spherical shock=-waves from two 50-g tetryl 
charges bh while figure 26 illustrates a Mach effect. The 
measurements were made primarily in the case of two ca. 1700=g 
spherical, cast, pentolite charges. In fig. 27 a typical 
plot is given. The average experimental curve indicates the 
predicted increase of resultant pressure § ‘with increasing 
angle of incidence @&. The quantitative discrepancy is of the 
order of magnitude of the observational error. (Exact agree- 
ment is hardly to be expected in view of the above theoretical 
assumption of constant pressure behind the incident shocks and 
in view of the experimental uncertainty of determining the 
peak pressure by a method of extrapolation.) Furthermore, the 
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