squared working into a known load was a measure of the power 
involved. By extension anything involving the square of the 
sample studied has been described in terms of power which ex- 
plains the origin of the term cumulative power density. Later 
on when actual wave power is studied, it will always be referred 
to as wave power in order to eliminate confusion. . 
To proceed with the definition of the integral given by 
equation (7.1),* in equation (7.6) the uw axis has been marked 
by a series of points, Op ysH arp zeeeee* Wore Such a division 
of the range of integration into a number of small intervals 
is called a net. The Bh are not necessarily equally spaced, 
and they are not necessarily rational points. Now form the 
sum of terms represented by equation (7.7) before the limiting 
process is applied... The first term is given, for example, by 
the square root of the difference (which is greater than or 
equal to zero) between E( p>) and E( py.) times the cosine of 
#,t plus W(t) where, as yet, w(y4 4) is not defined. 
The function, wy (p4)> can be defined in many ways. One 
definition would be to give a set of points between O and 27 
from which a value could be picked by some rule once V on+1 
was given, and the fact that the integral involved such a set 
of points would then make it a Lebesgue integral. Suppose then 
that such a rule is given for picking the value of W(p a43). 
Then the integral of equation (7.1) is the limit of the 
sum given by equation (7.7) as the mesh of the net approaches 
*For additional information, see Levy [1948]. 
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