way on the set of points in the record which determine the suc- 
cessive relative maxima and minima of the record. The probability 
distribution of this set of points may depend on the power spectrum 
in addition to the fact that the record as a whole is Gaussian. It 
is not too difficult to believe that the various ratios, 1/10 high- 
est waves to the 1/3 highest waves, etc; such as summarized by Snod- 
grass [1951] are all consequences of the fact that the records are 
Gaussian. The trouble with these methods of analysis and of attempts 
to extend them such as those described by Putz [1950, 1951] is that 
the features of the wave record are obscured by concentrating attention 
too sharply on the waves. Paraphrasing an old saying: "such methods 
of analysis cannot see the wave record on account of the waves." 
Similarly, the "characteristic" or "significant" period is a 
number determined from the time interval between successive relative 
maxima of the record if the relative maxima exceed a certain value. 
Given a high crest, the autocorrelation function says that the next 
crest is also likely to be high and that the next crest is most likely 
to occur at a time given by the first relative maximum after lag 
zero of the autocorrelation function. For a "swell" record the first 
maximum of the autocorrelation function has an amplitude which comes 
quite close to the original peak value and thus the "significant" 
period would have a useful meaning if the band width of the swell 
could be given. For a "sea" record the first relative maximum can 
be.quite low, which means that the "significant" period is not a 
very useful number at all. 
If the autocorrelation function in figure 38 is used to obtain 
the significant period of the pressure record studied at the start 
97 
