18 
51. For a plane rigid sea-bed 
the necessary boundary condition 
is that there is no particle 
velocity of the water perpendicular 
to the sea-bed. This condition 
is satisfied if the effect of the 
sea-bed is considered equivalent 
to an image explosion at E'', equal 
in every respect to the actual 
explosion at E in fig. 7. 
52. The pressure/time curve at 
any point P due to the original 
pulse and the reflected pulse 
would then be of the fom 
0 Cc 0' CF, in fig.8, corres 
simply to the addition of pressur 
time ourves of the form 0 C D and 
O' C' D' in fig. 6a, from a single 
explosion at distances E P and 
E'' P respectively. 
Fig./ - Reflection of pulse 
at sea=bed 53. In practice, no sea=-bed is 
completely rigid and the reflected 
pulse is smaller in magnitude than 
that indicated by the preceding assumption of complete reflection. 
Moreover, the sea-bed may distort the shape of the reflected pulse. 
In fig. 8 the portion 0' C F would then be replaced by the smaller 
and more rounded bmp O° GH. 
