CANADIAN FlhillElUE^ EXPEDITION, U)l',-l.j 267 



projection of the curve upon the equatorial plane; and, further, that the alternation 

 in the circulation of such a closed curve per unit of time amounts to 



dC _ dS 

 It -^'^ ~dt 



wnere ^indicates the alternation per second in the area of the curve's projection 



upon the equatorial plane. Where S is reduced, the curve assumes a cyclonic circula- 

 tion, while when S is increased, the circulation will become anticyclonie. 



Finally, the circulation is also influenced by the friction. For the effect of this, 

 Bjerknes has introduced the symbol li. As both the earth's rotation and the friction 

 as a rule oppose the distribution of density, Bjerknes gives the influence of both a 

 minus sign, and writes 



dC dS 



dt di 



This formula contains all that influences the circulation of the water in the sea. 



dt =^'-'-^ li -'' («)• 



12. SOLENOIDS IX THE CAXADIAX ATLANTIC AKEA. 



Bjerknes' circulation theory will, it may safely be said, play a prominent part iu 

 future oceanographical investigations, on account of the ease with which it may be 

 applied to hydrographical observation material, and the clearness and direct practical 

 value of the results thereby obtained. 



Its chief importance in the immediate future will be as a system upon which to 

 order and arrange the collecting of oceanographical observation material. The system 

 re(]uires, in this respect, certain conditions, of which those concerning the distribution 

 of density and specific volume have been excellently fulfilled by Dr. Hjort's measure- 

 ments in the Canadian waters, while those concerning the distribution of velocity 

 have as yet proved impossible of realization. 



I purpose, then, in the following pages to apply Bjerknes' circulation theory, as 

 far as can possibly be done, to the present material, drawing such conclusions as may 

 thence be arrived at, and finally indicating what yet remains to be done in order that 

 the syiitem may be utilized to its fullest extent, and by the gradual adaptation of 

 measuring instruments, methods of observation, etc., directed towards the solution of 

 still further oceanogTaphical problems. 



The weak point in the methods of observation hitherto in vogue is the system 

 employed for measurements of velocities. Bjerknes' theory demands two kinds of 



ds 



measurements in this respect: one for the calculation of 2<o -rr and the other for 



di 



that of Tl. An instrument for the former already exists,^ and all that remains here 

 is to arrange the observations in such a manner as to render them suitable for the 

 Ijurpose of calculating the influence of the earth's rotation according to Bjerknes' 

 theory. For the latter calculation, we have no suitable instrument as yet; it is, how- 

 ever, an easy matter to construct one, and to arrange the observations so as to furnish 

 the requisite material for calculation of B. 



As regards A, the material collected by Dr. Hjort from the Canadian waters is 

 in this respect beyond question the best that has ever been obtained from the atmos- 

 phere and the sea. Hjort's idea was to procure the fullest iX)ssible survey of hydro- 

 graphical conditions, spring and summer, in the North Atlantic area, and this, as it 

 proved, coincided entirely with Bjerknes' requisition as to get two complete and simul- 



1 Hans Pettcrson. A recording current meter for deep sea work. Quarterly Journal 

 of the Royal Meteorological Society, vol. XLI, No. 173, January, 1915. 



6551—21.^ 



