30 
896 
6. 
where @r is the acceleration of the fluid at T. The quadratic 
term in (5,5) vanishes in the acoustic anvroximation. Probably 
the only vlace where appeal to the acoustic approximation may be 
questioned is at the orifice where the material velocity may rather 
greatly exceed ite value in the incident pulse; but here the flow 
is one-dimensional and nearly incomvressive, hence 24 is small, 
and therefore the quadratic term in (5,5) 1s small also. Then, by 
(5.5) and (4,4) 
(5,6) pos apy Bf 4 ds 
(Te) 
where a, ie the acceleration of the fluid at the projection of a8 
on T. At the surface of the cauge.ap is the acceleration of A or 
of B. Elsewhere it ia not directly related to the motion of the 
gauge; but in our applications of (5,6), the surface B is usually 
taken so large that ite integral vanishes in Cy by retardation. 
(5,6) 18 therefore the desired exvression of the pressure in terms 
of gauge ccordinates. The corresponding expression for the pressure 
at greater distances in front of the gauge is by (4,5) 
(5.7) PP) = plP) + f(Q) - ee if + [a] AS 
amr 
(T) 
The M M Equatio 3 : 
The factor, 1/3, 1s correct for a spring of uniform density, 
ie probably satisfactory for a cylindrical vellet, and it is 
