OBSERVATIONS ON THE WAVES. 



31 



detennine the height, length, and velocity of the 

 waves. The results will be apparent from the fol- 

 lowing tabular view.* 



Oceanic birds were plentiful in our wake, and 

 gradually dropped off as we approached the tropic. 



* The height was determined by watching when the crest of 

 the wave was on a level with the observer's eye (the height above 

 the trough of the sea being known), either while standing on the 

 poop or in the mizzen rigging ; this must be reduced to one half 

 to obtain the absolute height of the wave above the mean level of 

 the sea. The length and velocity were found by noting the time 

 taken by the wave to traverse the measured distance (100 yards) 

 between the ship and the spar towing astern. In column 3rd, 

 the number 4 denotes a " moderate breeze," and 5a" fresh 

 breeze." 



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