WA VES. 25 



Those in the rear of the waves, as at A, are centres of departure 

 for particles which are constantly leaving them and moving 

 towards the points B on the faces or breasts of the waves. The 

 backs or windward surfaces of the waves are thus being con- 

 stantly lowered, through loss of water, whereas the fronts, or 

 breasts, are being constantly raised by the flow of particles 

 towards them. This lowering of the backs of the waves and 

 heaping up of their fronts is, in deep water, little more than 

 a vertical movement of the particles. The motion is, however, 

 delusive, and causes waves to assume the appearance of moving 

 bodily forward, and carrying with them a mass of water equal 



.Direction of propagation .^ 



*~fi ?f~l ~J 1 



v-V* ^ \ V. ^^> / 



( V v. *s<S J l 



FJG. 6. Diagram 1 showing motion of particles in a wave of oscillation. The small arrows 

 indicate the motion of the particles which form the wave, and illustrate the manner in which 

 they flow towards its breast and away from its windward surface, as described above . 



to their volume. It is, nevertheless, well known that only the 

 form and energy of the wave are transmitted, and not the water, 

 excepting to a certain extent in waves of translation, to which we 

 will presently refer. 



As waves pass into gradually shoaling water the friction of 

 the bottom becomes more and more felt by them, the motion 

 of the particles of water in contact with the bottom being most 

 retarded, and that of the others in a constantly diminishing 

 degree towards the surface. This causes a gradual change to 

 take place in the form of the waves, as shown by the sketch in 

 Fig. 7, p. 26. Their slopes, back and front, become steeper, their 

 crests more raised, and the orbits in which their particles 

 revolve become elliptical. Such waves are passing, by degrees, 

 from a state of approximate simple oscillation to one of more 



1 Copied, with some slight alteration, from a sketch which illustrates Sir G. B. 

 Airy'a treatise on " Tides and Waves." 





... 



