Chapter 2 



THE DIMENSIONS OF WAVES 



The dimensions of waves, by which their shapes and sizes are usu- 

 ally defined, are : 



a. Height, i. e., the elevation of each crest above the succeeding 

 trough, expressed here in feet. 



b. Length, from one crest to the next, also expressed here in feet. 



c. Velocity at which the wave form advances across the sea, ex- 

 pressed here in knots. 



d. Period, i. e., the length of time required for the passage of two 

 succeeding crests passing a stationary point, stated here in seconds. 



Many measurements, more or less reliable, of the dimensions of 

 waves have been made at sea in various parts of the world and under 

 various conditions. Among them we might mention, especially, the 

 series made by Lt. A. Paris on French naval vessels in the Atlantic 

 Trade Wind Belt and the southern West Wind Belt of the Indian 

 Ocean, in the East China Seas, and in the western Pacific ; by R. Aber- 

 crombie in the West Wind Belt of the South Pacific; by the officers of 

 the German research ship Gazelle in the North Atlantic, South At- 

 lantic, and Indian Ocean ; by G. Schott, during a voyage on a sailing 

 ship in the North Atlantic, South Atlantic, and Indian Ocean in 1891- 

 92; those by Lt. O. Gassenmayr of the Austro-Hungarian Navy on 

 the Donau in the Atlantic in 1895; those by V. Cornish in the North 

 Atlantic ; especially the very large series of measurements by Ameri- 

 can officers that were taken during the years 1883-87 and assembled 

 by Capt. D. D. Gaillard of the United States Army ; and the dimen- 

 sions derived by A. Schumacher, from stereophotogrammetric pictures 

 taken of waves during the Meteor' Expedition to the South Atlantic, as 

 well as from the liner Deutsehland in the North Atlantic. The dimen- 

 sions of waves have also been the subject of many theoretical 

 discussions. 



THE HEIGHTS OF WAVES 



The question, how high are the waves at sea, is one to which very 

 various answers have been given, partly because it is difficult to 

 measure wave heights exactly on shipboard, partly also because three 

 rather distinct problems are involved : the relationship between wave 

 heights and the character of the wind; the heights of the common 

 run of waves at different times and places; and the heights of the 

 largest waves that accompany severe and prolonged gales. 



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