1495 
The treatment developed in this paper affords a detailed 
description of the progressive changes taking place in the 
pressure wave during shallow water propagation between the region 
close to the charge, discussed by R. H. Cole’ » and the very 
long range effects treated theoretically by Pekeris®, and 
experimentally by Ewing® and his co-workers at Columbia 
University and the Woods Hole Oceanographic Institution. 
It should also be noted that when acoustic pulses 
are reflected from media of greater sound velocity at angles 
exceeding the critical, it is no longer possible to attach 
meaning to any single quantity described by the term "reflection 
coefficient." The reflection of the pulse so distorts its 
shape and amplitude that descriptions in terms of reflection 
coefficients become virtually useless. 
It is somewhat surprising to find that the naive 
approximation of the bottom as a fluid medium proves as successful 
as it does in predicting the experimental curves. In this 
connection it is interesting to note Dr. Ewing's observation 
(privately communicated to the authors) that even limestone 
bottoms are more successfully treated as fluids than as solids 
in his very long range experiments. 
