60 



Observations and Measurements of Ocean Waves 



than 3-9 m. The average period T is 8-6 sec; besides, T max = 121 sec, 

 T = 16-7 sec and T u = 4-7 sec. 



8. Scales of Sea Motion and Wind 



For practical purposes, the state of the sea (sea motion) has been defined 

 by a number from a scale divided into ten parts. The different steps of this 

 scale have been defined by international meteorological congresses and were 

 gradually improved. Unfortunately, different authors have used difference 

 scales which were not always comparable. The scales which are used most 

 often are the scales adopted in Paris in 1919 (Paris scale), the Douglas scale 

 adopted in Copenhagen in 1929 and the new scale adopted at the Inter- 

 national Meteorological Conference held in Berlin in 1939 (s^e Table 9) 



Table 9. State of the sea 



* As might exist at the centre of a hurricane. 



They are quite helpful in building up statistics of the wave movements 

 and wave measurements for a certain part of the ocean, provided the ob- 

 servations are extended over a sufficient length of time. We should not forget 

 that, like evaluating the wind force according to the Beaufort scale, the 

 evaluation of the sea surface by a number is not applicable to a certain point, 

 but it embraces the state of the sea over a very large area. Therefore, we 

 work with field values, and not with point values. This, however, is not a dis- 

 advantage, because in this way we evaluate the average state of a large sea 

 surface, which is more advantageous for practical purposes. 



Schumacher (1939, p. 82) has worked up the enormous number of 

 observations from the logs of the old sailing ships. These observations of 

 the state of the sea which extend over all oceans have been classified according 

 to the Paris scale of 1919. His results have been reproduced in Fig. 35 and 

 they show the frequency of the different state of the seas in particular parts 

 of the oceans. It is surprising to see that very calm and smooth seas are 



