885 
end (22.2) are comvared. There it is shown that if a baffle 
must be of thickness dy to satisfy the rigid-block criterion, 
(21.1), end of thieknees d, to satisfy the soft-block criterion, 
(22.2), then always 
(23.1) ee 
This inequality is true only if Pp c,/p¢ < 200; but this con- 
dition is always satisfied in vractice, e.g., for steel, 
Poor/Pe = 27. That is, it is only necessary to satisfy the soft 
criterion (22.2). In so doing one fails to satisfy the rigid 
criterion (31.1); but, as remarked in the previous varagravh, one 
gains nothing by exceeding the thickness dae If it had turned out 
differently, i.e., if the result had been da. < ~ then it would 
be vossible to use a thinner block than thet svecified in (22.2). 
As it is, an effectively infinite block should probably be de- 
termined exverimentally with(22.2) es a guide. (A typical value 
of d. is 50 em, corresponding to a gauge time, Og» of 200 micro- 
sec). 
24- It is then possible in principle to make the influence 
of the block on the piston negligible by giving the block a cy- 
lindrical form of length, d, end radius, Ry, where 
(24.1) a= 9% 
Ja Aaa 
8 
a 
Inertia and thickness having been considered, the principal re- 
(24,2) R, 
maining factor is the way the softness of the block allows the 
front face to move. 
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