1540 
10. Effect of gauge size on rise time and shape of shock wave which 
has undergone viscous attenuation. 
10.1 Owing to the low pressure amplitudes obtaining at ranges 
where viscous effects have become apparent, experimental 
measurements must be made with sensitive (and consequently 
large) gauges. It is desirable, therefore, to examine the 
effect of gauge size in distorting waves of the type illustrated 
in Figures 11 and 12. 
In view of the approximations already introduced into 
the theory, it is not worthwhile carrying out the analysis 
riéprously in terms of circular gauge shapes and equation (91); 
we rather introduce simplified forms for the step response 
and incident wave as follows: 
° »-w<t<o 
Relative step response of gauge, R(t) = t/m ,o<t<™ (113) 
al , "<t<o | 
o 6 ,-e0<t<o 
Relative pressure of incident wave, P(t) = y tenia) 
t/n ,o<< 14 
1-Ab) n <t<X 
Thus the step response is assumed to have a linear rise of 
duration m where m is the transit time of the pressure wave 
across the gauge, and the incident wave is approximated by 
a saw tooth shape with a linear rise of duration n and a 
decay-constant d ° 
To obtain the expected response of the finite gauge 
= 64 . 
