1493 
and this particular reflection is identical in form and 
amplitude with the incident wave, the various phase shifts and 
inversions having neutralized each other exactly. In general, 
of course, the cumulation will be such as to give more or less 
distorted forms depending upon the geometry and other para- 
meterse 
The experimental record in Figure 2b illustrates a 
case in which cumulative phase shift produces a reflection, 
Ms=i1,N = 2, which is an almost perfect reconstruction of the 
incident shock wave. 
3.5 The changing character of the wave with increasing range is 
also illustrated by the sequence in Figure 2. It is seen how the 
reflections become more distorted and how they increasingly 
interfere more strongly with each other and with the primary , 
shock wave as all the superposed disturbances get closer and 
closer together. 
The increasing interference is, of course, a consequence 
of the spherical nature of the waves, since in the case of truly 
plane waves "range" would have no meaning and the time intervals 
would be fixed by Qo, and the position of the point of observation. 
At very large ranges so many higher order reflections 
would overlap and interfere with each other that the simple 
treatment developed above would no longer be useful and the 
resultant wave would be better described in terms of the normal 
mode analysis of Pekeris®, 
Sngligres 
