1201 
agers 
the apnearance of two peaks requires a less direot comparison, 
viz., that of the total pressure which would obtain in the absence 
of the exponential decay of pressure and Af the waves were plane. 
This may be obtained by adding the second increment in pressure to 
the first peak,correcting both pressures to the same distance from 
the charges, From analogy to the reflection case, the pressure so 
obtained is equivalent to the total pressure behind the shock front 
upon reflection of a plane, step shock wave incident upon a rigid wall. 
This pressure, relative to the incident wave (1.e,, to the shock front 
from a single charge), 1s given in Table II, It may be seen that 
even in the absence of Mach interaction (L4 <pxprenp) the pressures 
from the two charges do not simply add acoustically, the ratios being 
greeter than 2. 
The gauges outside the plene of intersection indicate the width 
of the Mach region, Thus the disappearance of the second peak for 
G-2 at 72° and for G4 at 80.8° means that the Mach zone was at 
least 4 inches wide in the former case and over 8 inches wide in the 
Latter, It must be borne in mind, however, that a second peak would 
have escaped observation if it had been less than about 5 microseconds 
behind the first peak, 
The observed effective time oonstants are given in Fig, 2, They 
were obtained from the initial slope of the semi-log plots, The low 
values obtained in the range of oo in which maxiinum pressures ocour 
ere a measure of the abnormally rapid decay in this critical region. 
Momentum Integral, The evaluation of the momentum integral / pat is 
comnliceted by a “out~-off" in most of the pressure-time curves (See 
Fig. 11), This out-off is believed to be dve to the arrival at the 
gauge cf a rarefaction wave produced by the reflection of the shock 
wave from one charge off the gas bubbie of the other, In Table III 
this hyvothesis is applied to the observed cut-orf times in order to 
roughiy estimate bubble radii, The radii were calculated by assuming 
that ell waves traveled with sound velocity, The results are consistent 
with the bubble radii from smaller charges (3ee Section 2). 
Because of this complication, the impulse integral was evaluated 
out to both 218 and 560 microseconds, the former time being the 
shortest cut-off observed, Figs. 5, 7 and 9 show the values 
observed for {pdt within,2" outside, and 4" outside the plane of 
intersection, respectively, See also Table IV, At the shorter 
integration time, the gauges in the plane of intersection show no 
maximum, but instead a steady decline as the charges are brought 
together, “The other gauges show a slight small maximum but this 
is probably due to the smaller contribution of the wave from the 
second charge at smaller angles because of the arbitrary limitation 
of the integration to 218 microseconds, The slight minimum in the 
560 microsecond curves is believed to be due to the early out-off 
when the charges are close together (see Fig, 11). 
Energy Function, The quantity i. J pat 1s plotted in Figs, 6, 8 
and 10, Only the integrations tO 560 microseconds are given since 
those to 218 microseconds give essentially the same general curves, 
It is apparent that this energy function does not pass through any 
