1575 
the positive wave. The counterpart of equation (108) thus becomes 
9-6@ (10%) x w 2 ee 
aes ae ee 7 
AR Pee 2 4 (154) 
an equation differing from (108) only in sign but having an 
entirely different character. The differential equation (154) 
possesses no "equilibrium trajectory," so that it is necessary to 
select an appropriate starting point by some other means. It is 
natural to carry out the integration for the positive wave by (108) 
up to the point of reflection and subsequently by (154) for the nega- 
tive wave up to the point of interest, using the condition of con- 
tinuity of the “equivalent viscous distance" at the point oi reflection. 
The results of such integrations show that the fall time of the 
reflected wave is greater than the rise time of the direct wave only 
by an amount too small to be successfully distinguished by our measuring 
equipment. For example the fall time of the reflected wave froma 
4 lb. charge which reflects at 2000 ft. from the charge and then 
propagates for an additional 2000 ft. is psec: The rise time of the ; 
direct shock which travels the same total distance is 19msec- Both 
of these figures are of the order of magnitude of the transit time for 
the gauges used at this range. On the average, the observed fall 
times appear to be larger than the rise times, but for the reasons 
outlined in section 10.2 it is not possible to obtain reliable absolute 
values of these small intervals to test the theory quantitatively. 
~ 99 = 
