TuAwsoN] EFFECT OF WIND ON CURRENTS AND TIDAL STREAMS I9S 



The berg ice, from its great depth in the water, will evidently move 

 with the imder-current; and it will not be appreciably affected by the 

 wind. These bergs do not necessarily indicate the direction of the cur- 

 rent as affecting shipping, except when the surface current has also the 

 same direction. They show in reality the average direction the current 

 has, between the surface and tlio depth of their drauglit. They are thus 

 of much value as an indication of tJie general movement or circulation 

 of the water. 



The relation of the flat ice to the wind and current requires some 

 little consideration. It is, of course, just as true of this ice as of the 

 berg ice, that the greater part is under water; but, as it is almost always 

 in broken pieces, more or less piled and with upturned edges, the wind 

 has a much greater hold upon it in proportion to its total weight, than 

 on the berg ice. Even, when this is allowed for, its depth in the water 

 still gives the current a greater hold upon it than the wind has. For 

 example, if such ice is driftmg with a current in a given direction, and 

 the wind is blowing across that direction at right angles, the ice will 

 seldom be set more than two points, or three at the most, off the true 

 direction of the current. When the ice becomes soggy or water-soaked 

 and loses its edges, as it does later in the spring, it will set still more 

 correctly with the current. 



Wlien the surface current itself is moving in the direction of long- 

 continued or prevailing winds, as it often does in the Gulf, the flat ice 

 naturally follows the same direction too. Also in regions where the cur- 

 rent is tidal, and the ice in calm weather would drift as far in the one 

 direction with the flood tide as in the other direction with the ebb, the 

 direction in which it makes on the whole will depend upon the wind. 

 It is probably for these reasons that it is so often said that the ice drifts 

 vritli the wind ; although this merely expresses the result, without distin- 

 guishing between the relative influence of the wind and the current 

 upon it. 



There is also a direct effect which the ice has upon the strength of 

 the current in regions where the direction of the surface drift is under 

 the influence of the wind. The broken and upturned edges of the ice 

 give the wind a much greater hold upon the water than it otherwise 

 would have. Hence during long continued winds, the speed of the cur- 

 rent is appreciably greater than if the ice were not present. This is un- 

 doubtedly the explanation of the common belief which is expressed by 

 saying that " the ice makes its own current." Tt may be well to recall 

 that the weight of the ice itself is the same as the water which it dis- 

 places: and therefore, the wind has no greater mass to set in motion in 

 producing a surface current than if the ice were to melt and re-fill the 



