CANADIAN FISHERIES EXPEDITION, 1911^15 263 



there appeared the oblique strip which separates the heated water from the cooled, 

 answering to the under surface of the Gulf Stream in the sea. By means of an elec- 

 tric turbine, a current of air was then directed through a number of tubes set obliquely 

 to the surface of the water, producing a very effective tangential wind action upon the 

 same. The second diagram in fig. 45 illustrates the effect of the wind when blowing 

 in the direction of the artificial stream answering to the Gulf Streaan produced as 

 above described. The oblique strip, corresponding the lower surface of the Gulf 

 Stream, then approaches the horizontal, i.e., the Archimedean forces in the current are 

 here highly weakened, and contribute only in a very slight degree to propulsion of the 

 water. As a matter of fact, the strip can, by sufficiently increasing the force of the 

 wind, be made to .slope the opposite way, when the Archimedean forces will actually 

 oppose the progress of the current. On the other hand, with a wind in the opposite 

 direction to that of the current, as shown in the lowest diagram, fig. 45, the slope is 

 increased, the Archimedean forces being then greatly augmented. 



The meaning of this is not difficult to comprehend. The hot centre W produces 

 a certain quantity of warm water, and the cold centre K a certain amount of cold 

 each second, quite independently of the wind. By adaptation, consisting of change 

 in temperature, a state of things is soon reached when the cold centre consumes warm 

 water and produces cold at a rate per second exactly corresponding to the rate at 

 which the warm centre consumes the cold and produces warm. The quantity of water 

 flowing per second through any section of the current will be exactly equal to the 

 amount of water thus transformed. Whether the current be subjected to the action 

 of the wind or not, this quantity of water must flow on. In the case shown in the first 

 diagram, fig. 45, the current is opposed only by the internal friction of the water itself, 

 and the Archimedean forces have here only this resistance to overcome. In the second 

 case, the progress of the current is aided to a high degree by the action of the wind. 

 The result of this is, at first, an acceleration of the current ; this, however, soon causes 

 the oblique stratum to take up a more horizontal position, in consequence of which, 

 the Archimedean forces are so diminished that their motive power only sufiices to 

 propel the requisite quantity of water when aided by the action of the wind. Finally, 

 in the third case, where the forward movement of the water is greatly hindered by the 

 wind, the current is at first retained, then, with the consequent increased slope, the 

 Archimedean forces attain a higher degree of intensity, until at last they furnish 

 motive power sufficient to propel the due quantity of water despite the resistance of 

 the wind. 



From this we see how insignificant is the part played by the wind as a motive 

 I)ower in currents of this nature. 



11. BJERKNES' CIRCULATION THEORY. 



The Bjerknes' theory of circulation, with the clear and profound insight which it 

 displays, is in my opinion so eminently valuable an adjunct to the study of hydrogra- 

 phical phenomena that I have thought it necessary here to give a general idea of the 

 principles contained therein, inasmuch as these bear directly upon marine conditions. 

 I have endeavoured, in this survey, to keep to the simplest possible mathematical for- 

 mulae only; readers wishing to follow the entire process of deduction and examine for 

 themselves the manner in which the results are arrived at, may refer to Bjerknes' own 

 works on the subject, in particular to his comprehensive treatise on dynamic meteor- 

 ology and hydrography, published by the Carnegie Institute, of "Washington, U.S.A. 



We may commence with Bjerknes' analysis of the Archimedean forces. As a 

 result of this analysis it is shown that the measure of the forces in question may be 

 taken as represented by the number of parallelograms formed in a hydrographic section 

 by the intersection of the isobars with the isosteres. It is here presupposed that the 

 figures in question are drawn for each whole unit of pressure or specific volume. Each 



