OX SHIP WAVES. 489 



work I have already referred. Fig. 12, Plate 82, 

 shows a perspective vie\v of echelon waves taken 

 from Mr. William Froude's paper, " Experiments 

 upon the Effect Produced on the Wave-making 

 Resistance of Ships by Length of Parallel Middle 

 Body''' {Institution of Naval Architects, vol. xviii. 

 1877, page 77). 



The three diagrams from Mr. White, Figs. 6, 7, 

 and 8, Plate Si, show profiles of the thwart- ship 

 waves of various ships, at different speeds. Look 

 first at Fig. 6, showing *.the wave profile for 

 H.M.S. Curlew at a speed of nearly 15 knots an 

 hour. Note how the water, after the first eleva- 

 tion, dips down below the still-water line ; rises up 

 to a ridge at a distance back from the first nearly 

 but not exactly equal to the wave-length corre- 

 sponding with the speed ; and then falls down 

 again, experiencing various disturbances. From 

 the appearance of the waves raised by ships going 

 at high speeds, we may learn to tell how quickly 

 they are going. The other day, at the departure 

 of the fleet from Spithead after the great naval 

 review, a ship was said to be going at 18 knots, 



