VELOCITY AND PERIOD 33 



It is evident from table 15 that the relationship between the strength 

 of the wind and the velocity of the waves is not a constant one through- 

 out the development of the latter. Thus the statement sometimes made 

 that the velocities of storm waves average about 0.8 as great as that of 

 the wind would apply, theoretically, to a 20-mile wind only while the 

 waves were about 15 hours old; to a 30-mile wind only when they were 

 about 25 hours old; to a 40-mile wind only while they were about 35 

 hours old. The calculations summarized in table 15 also show the 

 velocities of the waves produced by a uniform wind of any given 

 strength as rising somewhat higher, eventually, than the velocity of 

 the wind. But the few observers who have measured the velocities of 

 storm waves at sea, in relation to the wind, have reported that the 

 advance of the waves is usually somewhat lower than the velocity of 

 the wind as long as the latter is still rising, or as long as it is still 

 blowing at its peak strength. Thus Schott reported the velocity of 

 the wind as varying between 1.17 times and 1.51 times (average 1.32 

 times) as great as that of the waves, on ten occasions when the waves 

 were measured and the strength of the wind estimated every 2 hours 

 by the Beaufort Scale. 8 Similarly, Lieutenant Paris, of the French 

 Navy, found the velocity of the wind to average about 1.4 to 1.7 

 times as great as that of the waves in stormy weather when a heavy 

 sea was running. 9 Again, Capt. H. F. David, of the S. S. t'orinthic, 

 estimated the average length of the waves in August 1907 in the south- 

 ern Indian Ocean between Kerguelen and St. Paul Island as about 

 675 feet, corresponding to an average velocity of 40 statute miles per 

 hour, when the wind was logged as 9, Beaufort, or about 44 statute 

 miles per hour (Cornish, 1910, p. 112). Cornish has reported wave 

 periods corresponding to velocities of about 41 knots in the Bay of 

 Biscay during a very strong gale, when the ship's officers estimated 

 the strength of the wind as somewhat greater than 9, Beaufort, or 

 something like 52 knots (Cornish, 1934, p. 4). And waves advancing 

 at 48 to 55 knots (as calculated from their estimated lengths and meas- 

 ured periods) were observed from the U. S. S. Ramapo, in the central 

 part of the North Pacific during a February gale when the average 

 velocity of the wind was 60 knots as recorded by anemometer. 1 " 

 Zimmerman, however, reports several cases of storm waves running 

 faster than the wind. 11 



The explanation for the greater frequency of waves running more 

 slowly than the wind probably lies in the fact that most observations 



" Schott, Gerliard. 1893. Uber die Diniensionen der Meereswellen. Festschrift Ferdi- 

 nand Freiherrn von Riehtofen znm 60. Gelmrtstaj;. Berlin. i>. 253. 



9 Paris, A. 1871. observations sur l'etat de la hut recueillies a bord du Dupleix et de 

 la Minerre. Rev. inarit. colon, vol. 31, p. 121. 



10 Whitemarsli, R. P. 1984. Great sea waves. Proc nav. inst. vol. 60. p. 1100. 



11 Zimmerman. E. 1920. Aufsuchunjr von Mittelwerten fiir die Formen austrewachsener 

 Meereswellen anf Grund alter and neuer ReobaclituiiKen. Sohiffbau. vol. 21. pp. 666—668. 



