AND OTHER WATER WAVES 67 



Throughout the whole of the nine weeks of ex- 

 ceptionally stormy weather which is covered by 

 these charts I cannot be sure of any greater effec- 

 tive length of fetch of wind than 600 geographical, 

 or 700 statute, miles. This is the wave-making 

 length of wind-fetch for the North Atlantic which 

 we have to compare with the 259 geographical or 

 289 statute miles of Lake Superior. The wave- 

 making effect of a strip of wind of 600 geographical 

 (700 statute) miles long on the mid-Atlantic is, 

 however, increased by the swell which is always 

 entering at the weather end. This result agrees 

 with the conclusion already arrived at that Scoresby 

 observed, at 600 geographical miles from the wind- 

 ward shore, waves of the greatest height producible 

 in the Atlantic by the then force of wind. 



The Numerical Relation between Length of Fetch 

 of Wind and Height of Storm-waves 



Thomas Stevenson's empirical formula ( height of 

 wave in feet = i .5 x square root of length of fetch 

 in geographical miles) was shown by him to apply 

 to distances of rather more than 100 geographical 

 miles. Colonel Gaillard observed waves 23 feet 

 high in the Duluth Canal with a length of fetch 

 of 259 nautical miles, the height calculated from 

 Stevenson's formula being 24. i feet. The same 



