As a first step, let us consider waves with long,
parallel crests but which differ in height, for example,
the profile as shown in the top curve of Figure 1.12.
Although this curve looks fairly regular, it is certainly
no longer the profile of a simple sinusoidal wave,
because the height is not everywhere the same, nor are
the horizontal distances between crests. This profile,
however, can be represented as the sum of two simple
wave profiles of slightly different wavelength (see I and
II in Figure 1.12). In adding the vertical deviations of I
and II at corresponding points of the horizontal axis, we
obtain the vertical deviations of the sum of wave I and
wave II, represented by the top wave profile in Figure