depend upon, among other things, the assumption that the decrease 
in wave height is caused by friction against the air. The width 
and the duration of the storm are not considered. Groen and 
Dorrestein [1950] attribute the decay of waves to eddy viscosity 
in the water, but again their theory does not account for wave 
dispersion and lateral spreading. The theory discussed in this 
paper predicts greater decreases in wave height simply due to 
dispersion and angular spreading from a storm of finite width and 
duration than are predicted by the Sverdrup-Munk theory without 
these considerations. 
Storms are of finite width and duration. A storm which is 
wide compared to the decay distance but which lasts a relatively 
short time would cause waves at distant points which decrease in 
height like 1//R simply due to dispersion. A storm which is narrow 
compared to the decay distance but which lasts a long time would 
cause waves which decrease in height like 1/VR simply due to ) 
angular spreadinz. Other small, short duration storms would be- 
have differently. Storms which cover a large area and which last 
a long time would behave still differently. The curves in Here 
Pub. No. 604 are based on wave observations from many storms of 
many different widths, durations, and fetch lengths. Consequently, 
the curves average in many errors even if there is some slight 
loss due to friction. 
From these considerations, and since the significant height 
and period have been shown to be inadequate in many other respects, 
it must be concluded that the decrease of wave height with distance 
traveled can best be explained by the methods derived herein and 
=249N— 
