O.V SHIP \VAVES. 485 



waves arc infinitely steep ; practically they are so 

 steep that the boat generally takes in a little 

 water, and is sometimes capsized. There is a 

 distance of perhaps a couple of feet from crest to 

 crest, and the wave is so steep and " lumpy " on 

 the outer border of the echelon that there is 

 frequently broken water there fifty or a hundred 

 yards from the ship. One point of importance in 

 the geometry of this pattern is that each echelon 

 cusp, represented in Fig. 48 at B or D, bisects the 

 angle between the flank line AB or AD and the 

 thwart-ship line BD : the angle in question being 

 70 32' (90 -- 19 28'). An observation of this 

 angle was actually made for me by Mr. Purvis. 

 He observed, from the towing of a sphere instead 

 of a boat (so as to get a more definite point), the 

 angle between the flank line AB and the direction 

 of motion CA, and found it to be 19^. The 

 theoretical angle is 19 28', and we have therefore 

 in this observation a very admirable and interest- 

 ing verification of the theory. 



The doctrine embodied in the wave-model may 

 be described in a very general way thus. Think 



