516 Mr. A. J. Robertson on the Positive Wave of 2 reinstation. 

 When #=0, 



When x = k or — &, t — 0, 



time from rest to rest = i / -— — . it ; 



V 3g 



and this being independent of k, considering AB = a-fZ; as 

 constant, the oscillation is isochronous. 



The Wave of Translation. 



PA. 



ff G 



Let AEB be a wave, AB the level of repose, QN a hori- 

 zontal line bisecting EC in k. 



Let AM — #"iAC = L 



PM-j/JEC = 2/c /. E#=K! = ifc 



AG = a 



CDxDH=| volume of generator =V 



V 

 .-. CD= -. 



a 



Let afbe a thin column taken anywhere in the still water. 

 The pressure on any particle is as its depth below the surface, 

 but being the same in all directions, the particle remains at 

 rest. But at A, the exact commencement of the wave, we 

 have on one side of AG a column pg slightly higher, whilst 

 that on the other side has the same height ; there is there- 

 fore an unbalanced pressure in direction Aa. The immediate 

 effect on the column AG is to raise A; for until the pressure 

 can be communicated through it to the water beyond, that 

 water is the same as if it were solid. The column AG when 

 raised exerts a pressure in its turn upon the next one, and 

 causes it to rise in the same manner. Thus the commence- 

 ment of the wave travels forwards with a velocity which de- 

 pends on the ease with which the pressure can be propagated. 

 This ease depends partly on the resistance to being raised 

 offered by the column itself, and partly on the forward move- 



