CANADIAN FISHERIES EXPEDITION, 1914-15 



233 



Another maximum of stability occurs at somewhat greater depth where the transition 

 from the light coastal current to the heavier subjacent layer oc(«s. This is shown 

 in fig. 9 f . 'vl 



All these features, together with otliers, are illustrated in p^^^es XII and XIII. 

 The diagrams for stability are, as will have been seen from the foregoing, extremely 

 instructive when discussing the condition of the sea and the causes which produce the 

 various hydrographical situations there occurring. 



6.— INFLUENCE OF THE WIND UPON THE MOVEMENT OF SEA-WATER. 



In chapter 3, the various effects of the wind upon homogeneous water and upon 

 water in layers, has already been shown, vide figs. 4 and 6. Still more remarkable is 

 the action of the wind upon water in which the specific gravity increases continuously 

 with the depth. Let fig. 10 be a vertical section through a sea basin containing such 

 water, the horizontal lines 1-7 representing the isosterics. We presume that, for the 

 time being, no other forces are at work here beyond that of gravitation, and that the 

 water is at rest; the isosteric surfaces will thus lie perfectly horizontal. In fig. 10, the 

 isosteres are closest at the surface of the sea, where the stability of the water will in 

 eonsequene-e be the greatest. Fig. 9 c gives the diagram of stability for fig. 10. If now a 

 wind commence to blow, a displacement of the upper water will occur, this following 

 the direction of the wind; as, however, the water particles belonging to an isosteric 

 surface cannot leave the same, and as no water can penetrate through these surfaces, 

 the effect of the wind in this case will be confined to the deformation shown in fig. 11. 



Fig. 10. — Stable sea water in eciuilibrium. 



Fig. 11.— Influence of ilie wind on stable 

 .sea water. 



The isosteric surfaces retain their individuality, and the volume of water between them 

 remains unchanged despite the wind. The displacement of the water in the direction 

 of the wind causes the isosteric surfaces to slope more and more, giving rise to a strong 

 system of Archimedean forces, which tend to drive the surface water back against the 

 wind. These opposing forces continue to increase, until at last the water no longer 

 flows in the direction of the wind; a state of equilibrium is reached, and from the 

 magnitude of the Archimedean forces required to bring about the same, we may sub- 

 sequently calculate the force originally brought to bear by the wind itself. When the 

 wind grows fainter, or ceases altogether, the Archimedean forces drive the water back 

 in a direction opposite to that previously followed by the wind. As a rule, the water 

 now flows back too far, so that the isosteric surfaces slope the reverse way. This gives 

 rise to new Archimedean forces which send the water back once more in the original 

 direction of the wind. In this way the backward and forward movement may be 

 6551—19 



