SHOCK WAVE MEASUREMENTS 269 



increase rapidly with distance, as is evident either from this approxi- 

 mation or from Fig. 7.22, but for distances up to several hundred feet 

 have a very small effect on the wave front. The only circumstances in 

 which the small differences at short ranges may have significant effects 

 are probably in explosion depth ranging methods depending on meas- 

 urements of time differences (see section 10.3), but even in such meas- 

 urements the errors are unimportant for ranges up to several hundred 

 feet. These statements and calculations apply only to these ranges 

 and should not be extrapolated, but do give an estimate of the order of 

 the effects and the distances at which they must be considered more 

 carefully. 



