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INTRODUCTION 
1. A theory of dianhragm gauges has been developed by Kirk- 
wood (1). A theory of piston gsuges has been given by Hilliar 
(2) and by Hartmann (3), but their work ignores diffraction. 
This report gives a descrintion of viston gauges which does not 
neglect diffraction. A piston gauge is to be interpreted as a 
ball-crusher gauge, a Hilliar gauge, or a Hartmann momentum 
gauge, and in these calculations there is no essential difference 
hetween then. 
2. The essential element of a ball-crusher gauge (Fig. 1) con- 
tains a steel piston, one end of which touches a small copper 
ephere. The other end of the piston is exposed to the explosion. 
When the shock wave falls on it, the piston is driven forward 
and deforms the ball. The strength of the shock may be measured 
by the deformation of the ball. The Hilliar tyne of geuge is 
similar, but it mey contain several pistons of different lengths. 
Each of these may have a Gifferent time of free travel before 
striking an anvil and deforming a cylindrical vellet, carried 
Fic. J. on ite front face. The 
Hilliar gauge supplies in- 
: — = 4 
WY COPPER SPHERE formation on the time-variation 
PISTON of pressure, since its pistons 
have different response times. 
Finally, e Hartmann momentum gauge contains ea single viston of . 
such long response time that it may measure the total momentum 
Ey pee 
