CANADIAN FlsHt:iUi:>i EXPEDITION, Wl.'rlo 



235 



depth in the sea is often found, not at the j^urfaee, hut at some distance beneath, 

 rule, fig, 9 d, and plates XIT and XIII. 



Fig. 14. — State of sea water after a storm. 



Obviously the greater the stability of the water, the more difficult will it be to 

 make the surface water jibe over in this manner; whence again it follows, that the 

 phenomenon is more easily occasioned in winter than in sunnner. In other words, 

 the surface water exhibits a far greater power of resistance to the wind in summer 

 than in winter. This peculiarity has been remarked by fishermen on the west coast 

 of Sweden, who declare that the sea-water is harder or heavier in summer than at 

 other times of the year. 



With water in layers, the matter is naturally far simpler, vide fig. 6, than where 

 the density increases continuously with the depth. Even in such stratified water, 

 however, many dynamically and hydrographically interesting phenomena may occur. 

 It is instructive to begin by producing such experimentally, and afterwards observe 

 the corresponding realities in the sea ; by this method, as by no other, it is possible 

 to arrive at an intimate understanding of oceanographical phenomena. 



Figf. 1 5.— Experiment illustrating action of wind ujion 

 water in strata. 



I purpose now to describe some experiments which I have carried out as illus- 

 trative of the influence of wind upon stratified water. A tank 100 cm. long, 25 em. 

 deep, and 3 cm. across, with glass walls, was filled to a height of 10 cm. with fresh' 

 water. By means of a thin tube, heavier salt water was then introduced beneath this, 

 making another layer 10 cm. deep. With the aid of an electric arc lamp, a picture 

 of the tank was then projected on to a white sheet, whereby the separating surface 

 between the two water layers was rendered very distinctl.v visible, owing to the refrac- 

 tion of the light. As long as the water was left midisturbed, the boundary line was 

 horizontal, and the layer of uniform thickness. By means of a blower, a strong 

 current of air was then driven across the surface of the water, when the separating 

 line took the direction shown in fig. 15. A point especially worthy of note is the 

 depression at that end of the reservoir to which the wind was directed. This is 



6551—19* 



