\\ 
870 
for the vressure in terms of this information is calculated from 
Kirchhoff's theorem. 
9. Before giving the adavtation of Kirchhoff's theorem just 
mentioned, it is convenient to introduce the following notation. 
The surface which the gauge presenter to the shock consists es- 
sentially of two narts: the face, A, of the niston (pistons), 
and the face, B, of the block, in which it moves (see Fig. 3). 
B may be extended by a baffle. A, of course, moves rather rapidly 
while B moves much more slowly. At the time, t = 0, when the shock 
vulse firet strikes the gauge, A is flush with B, Let the infinite 
plane containing A and B at t +0 be Ty. At leter values of t let 
Fig, 3 the projectiona of A and B on T be 
A and B. Let the rest of T be 
fo) fo) fo) 
Co» so that 
Zz B B & + + 
At (9.1) T) = A, Ss & 
4 A UJ 6 
\ Gar te Als. Cc. T. Let the broken, moving surface, 
WE: THROWN vi T, be defined by 
\BACK BY GAUGE, ; 5 
me ee (Oe 2} T=) AxtCB C,: 
~~ _—_—— 
Then in terma of the surfaces, z. and T, the fundamentsl expression 
for the pressure is (for proof see avvendix, varagravhs ]. - 5.) 
(9.3) v= 2.0 Pe £ i ta,(4-£)das 
Cr) 
where 
p = total vreasure, excluding hydrostatic vressure, 
at any time on the plane TS at any point which is 
behind the wave front thrown back by the gauge. 
p. - value of the pvressure at this point if no gauge 
were vresent. 
Ba ee 
