512 
- 16- 
These results indicate quite definitely that the law of variation of P max with distance is 
given by P aoe cc + for an 184 1b. charge over a range from 20 to 45 feet. {t should be noted, in 
D 
applying the above method, that the accuracy diminishes “er *) approaches unity, and its logarithm 
' 
zero, when the value of x (in formula 3, page 15) becomes ateqrinatas {In order to obtain an accurate 
result, the value of 0, x D0, should be great compared with om X D. consistent with the condition that the 
values of 3, 5, 5, 5, 8, should al) be sufficiently great to be Genre le of accurate measurement. 
it is considered that the relation between P mas © D obtained in this manner is considerably more 
reliable than that obtained by the statistical average method referred to above. |t is regretted, however, 
that no opportunity occurred during the investigation, of repeating the triple-gauge experiment with larger 
Charges - only isolated observations having been made in such cases. The experiment appears to be well 
worth doing, however, to establish if the inverse distance law, which holds so exactly for 194 1b. charges, 
is equally accurate for larger charges. Except in the region very close to the charge, perhaps, there 
appears to be no physical re son why this should not be so. Typical records are shown on Sheet || Records 
a and b. Record 'a' was obtained from an 184 1b. G.C. Charge, whilst in 'b' a 100 1b. T.N.T, Charge was 
used. 
(bd) Variation of P ... with Weight of Charge. 
This relation is one which is considerably more difficult to determine for now we can rely only on 
the average of a number of shots. Individual variations of maximum pressure for charges of the same 
weight and composition and packed in similar containers are considerable. Thus for the specially prepared 
T.N.T. Shots variations in Pe from the mean value for a particular weight of charge were, in extreme 
cases, as high as 20%; the mean variations of course were considerably less. Then again, with small gun 
cotton charges the extreme variation of Prax was approximately 30%, the mean variation being about 5 or 
10%. The necessity for firing a large number of charges to obtain a reliable average value of trae is 
apparent. 
in order to reduce all Charges and records to the same basis of comparison the inverse distance 
law has been assumed. AS we have seen in (a) above this is probably true for all sizes of charge at the 
distances with which we are mainly concerned (viz. 10 to 60 feet from the charge). In Figure 16a are 
plotted the values of log Peay (at unit distance, 1 foot from charge) as a function of log w, abtained 
from the analysis of 148 p.e. records. The number of individual observations, of which each point on 
the curve is an average is indicated. Considerable weight must be attached to the points corresponding 
to 24 1bs., 18% lbs. and 100 lbs. charges, for these represent mean values of 38, 70 and 24 observations 
respectively. It will be observed that all the points lie on or close to, a straight line represented 
by the relation 
log max 0.38 log W+ 4.08 
r 
© Prax 
12,000 w°38 lbs/sq.in. at 1 foot distance from a charge 
of weight W lbs. of T.N.T. gun cotton or amatol, 
OF seeeee 
