23 107 
a l-oz. piston, that is to say, the velocity it would have if acted on by the same 
pressure up to the same moment, is v= MV. ‘Lhe results are now in the form 
postulated in the first paragraph of this section, expressing the velocities v that a 
1-oz. piston would have acquired at distances s from its starting point, and the rest 
of the calculation is quite straightforward. 
The result is shown graphically in Fig. 33 as a series of rectangular steps 
through which a curve has been drawn in such a way as to leave out as much as it 
takes in. It will be seen that the steps form a very regular series (as they do also in 
the numerous diagrams illustrating Part I. of this report), and that, they provide a 
thoroughly definite basis for the greater part of the curve representing the decay ot 
pressure. On the other hand, it is clear that the steps in Fig. 33 do not give any 
positive indication of the form of the pressure curve during the first two ten- 
thousandths of a second, when the pressure isa maximum. ‘This part of the curve 
might have been drawn, without inconsistency, in quite a different way from that 
shown; for example it might have been drawn as indicated by the dotted lines. The 
determination of this part of the curve was effected by gauges of a rather different 
type, which are dealt with in the next section. 
It may be pointed out that it is not always necessary or desirable to make use of 
all the 10 sizes of piston shown at the top of Table V. The GB gauges, with the 
83-inch and 6}-inch pistons, were generally omitted, being unnecessary except in 
the case of very big charges, and experience also showed that nothing was lost in 
most cases by omitting the 43-inch piston. 
For comparison with Table V., the results of a number of other shots, all giving 
time-pressure curves of quite different character, are shown in a condensed form in 
Table VI. 
