recordings of sea surface ware heights from which discrete values 

 are scaled at equidistant time Intervals. The most striking feature 

 of the results of the mathematical analysis seems to he that the 

 wave patterns at the sea surface are dominated by more than one 

 "cyclical component" In most cases, which agrees with the findings 

 of the author. But In his notes on his work, H, R. Selwell points 

 out that the autocorrelation structure of data containing more than 

 one cyclical component becomes complicated and usually does not per- 

 mit Identification of the periods Involved, Its use Is limited to 

 a means of revealing the presence of more than one period, and 

 further Information concerning the Identification need be obtained 

 by some form of a Fourier Transform of the autocorrelations Into a 

 power apectrmn. One may look forward with Interest to the results 

 of analysis of Selwell 's surface observations In 1950. 



Another method for observing the state of the sea under differ- 

 ent conditions, particularly from ships under way, Is based on stereo- 

 photogrammetrlc pictures. This method [2] clearly reveals the com- 

 plicated configuration of the wind affected sea surface, and makes 

 possible exact morphological measurements, though the present possi- 

 bilities of this method are limited too. It Is a rather expensive 

 method and there are not many observations available at present, A 

 recent summary of the results obtained and an outlook on future de- 

 velopments with respect to stereophotogrammetrlc wave pictures In 

 rapid sequence by A, Schumacher [3] shows that the Improvements of 

 this method may be expected to prove very useful In future work. 



Besides these more expensive methods, there are several simple 

 methods of measuring waves from ships under way by direct obser- 

 vations. Compared with some highly developed technical methods 



