24 HARBOUR CONSTRUCTION. 



Scott Russell's experiments as recorded in the report of the 

 seventh meeting of the British Association were conducted on 

 somewhat similar lines to those of the "Webers, inasmuch as 

 troughs having glass sides were used in each case. Those used 

 by Scott Russell were, however, of much larger dimensions than 

 those employed by the Webers, and very sensitive appliances 

 were provided for observing and recording the heights and 

 velocities of the waves, as also their shape, the movement of the 

 particles forming them, and other points of interest. 



It would be difficult to devise a more illusive spectacle than 

 that presented by a series of large passing waves, it being almost 

 impossible to divest the mind of the idea that the volume of 

 water forming each wave is actually advancing. 



In watching waves from some such position as a pier-head 

 or staging, as they pass shoreward, this feeling seems to be 

 intensified, the eye naturally following them in their course, and 

 they retaining their individuality in a remarkable manner, until 

 they finally break upon the shore. 



If, however, instead of watching the waves themselves, we 

 fix our attention upon some free object floating upon the surface, 

 it will soon become evident that, instead of passing onward with 

 the waves, it oscillates between certain points, the distance 

 between which bears a fixed relation to the length of the waves 

 between crest and crest. 



Any onward movement of such floating object, which may be 

 caused by the action of the wind upon it, or by any current 

 which may exist, must, of course, be duly allowed for. 



Theoretical investigations, supported by the carefully con- 

 ducted experiments above referred to, show that the circulation 

 of the particles of water in waves of oscillation is approximately 

 that indicated by Fig. 6. 



The long feathered arrow denotes the direction of propa- 

 gation, and the shorter unfeathered arrows show the movement 

 of the particles of water, which, in a wave of oscillation, is 

 nearly such as would be produced by rolling circles, having their 

 diameters equal to the height of the waves, trough to crest. 

 The form of the waves is therefore approximately cycloidal. 



It will be noticed that the particles in the troughs of the 

 waves move backward, while those forming the upper portions 

 of the waves move forward. The points indicated in the dia- 

 gram by the letters A and B respectively are neutral points. 



