AND OTHER WATER WAVES 39 



130 feet, using the length of the promenade deck 

 as standard of measurement. This estimate is quite 

 out of harmony with the successive observation of 

 following waves. The speed of the vessel was 

 14 knots and the waves travelled past the ship at 

 a very considerable speed. They succeeded one 

 another at an average interval of 17 seconds. 

 This determination by itself does not permit 

 the wave-length to be calculated from a 

 simple formula, 1 but it is satisfied by a true 

 period of 8 to 9 seconds with length of 328 to 

 415 feet. Seven seconds (with a wave-length 

 250 feet) is definitely too small, and 10 seconds 

 ( with wave length 5 1 2 feet ) is definitely too 

 much. It is quite inconsistent with a length of 

 130 feet, which corresponds to a speed of only 

 i 5 knots, which is scarcely greater than that of the 

 ship, and it seems likely that this estimate of the 

 wave-length was in fact due to the transverse 

 waves caused by the ship's own motion, which for 

 her then speed of 1 4 knots have a length of 1 1 o feet. 



It appears, therefore, that the average wave- 

 length was not less than 328 feet (an 8 -seconds 

 wave). 



The wind was westerly, and the sea-room about 



1 It can be calculated, however ; see Monthly Chart, North 

 Atlantic, September, 1909, published by the Meteorological 

 Committee. 



