SNOW-WAVES AND SNOW-RIPPLES 157 



with the profile, which is all that is generally studied 

 in waves. 



The general form of an eddy can be observed 

 by fixing a board in a vertical position athwart a 

 stream, the board being just submerged. The con- 

 taining curve of the eddy is then easily traced by 

 the disturbance on the surface of the water. 

 There is seen to be eddying disturbance for a 

 short distance up-stream; its margin passes close 

 to the edge of the board in a direction slightly 

 inclined outwards, the greatest width of the eddy- 

 curve being a little to leeward of the obstruction. 

 From this position the border of the eddy closes 

 in very gradually, so that the tail of the disturbance 

 is situated far to leeward of the obstruction. The 

 distance from the shoulder, or position of 

 greatest width, to the tail is several times 

 greater than that from the commencement of 

 eddying on the weather side to the shoulder. The 

 outline as one looks down upon the surface of 

 the water is similar to that of fish as we see them 

 from above lying head up-stream. The eddy-curve 

 (on which, as I shall endeavour to show, sand- 

 dunes, snow-waves, and snowdrifts are moulded) 

 is the boundary-line on either side of the axis of 

 the eddy, the curve being precisely repeated, as 

 in a reflection, by the other side. When I refer 



