^-B 



23 



RESOLUTION OF FORCES IN GRADIENT CURRENTS 



It has been pointed out in the previous section that the effect of rota- 

 tion tended to deflect currents to the right in the Northern Hemisphere. 

 This quasi force can be represented by a vector of a certain magnitude 

 which lies 90° to the right of the current. If we let the line AB, Figure 1, 

 represent a more or less steady current of sufficient size to give the 

 water particles a translatory path, then the effect of terrestial rotation 

 may be shown by the line AC, Figure 7. Since the rotation effect 

 is always present, as represented by the line AC, it follows that the 

 only condition under which a current can flow, stream, and be pre- 

 served, is fulfilled by a force or system of forces (when friction is dis- 

 regarded) which acts equal and opposite to AC, and is represented in 

 Figure 7 as the line AE. AE illustrates the force characterized as 

 due to varying mass and pressure, 

 and is measured by the equated 

 values of the three variables — >'■ 

 gravity, 'pressure, and specific vol- 

 ume. It is, moreover, the impel- 

 ling force of such gradient currents 

 (i. e., currents resulting from an 

 obliquity of equiscalar surfaces) ; 

 and it should be remarked here q 



that this driving force is to be no. 7— a diagrammatic front view showing the 



sought not back along the current's ^^^.tW^ positions of the major elements belong. 



. ,., , ing to a steady gradient current. AB represents 



course to a riVer-llke source, but the path of flow of the water particles; AE, the 



it alwaVS lies on the right hand position of the forces due to Archimedean tend- 



... ^ . encies which impel the current; and AC the po- 



Stretchmg along the entire extent sltlon of the quaslforce of earth rotation in a 



of flow. The Gulf Stream, for ex- P^^^e ^° to t^e right (in the northern hemi- 



. sphere) of the direction of the current 



ample, as it lollows a general path 



around the periphery of the North Atlantic basin, is energized 

 along the shores of Europe (a fact which is just as vital for 

 its propagation) as well as receiving propulsion in the Caribbean. 

 Where the velocity is relatively great, there the dynamic gradient 

 is correspondingly steep, and without such energy distributed around 

 Atlantic slopes, the Gulf Stream would directly disintegrate. If we 

 divide gradient currents into the forces which combine to give flow 

 to the water particles we have (1) dynamic inequalities due to vary- 

 ing densities, and (2) the effect of earth rotation, each one of which 

 acts in a plane perpendicular to the path of the moving water parti- 

 cles. Since (1) and 2) lie in the same plane, and inasmuch as the 

 acceleration of the closed curve ABDC (see fig. 6, p. 22) (represented 

 by the line AC, fig. 7) has been determined, let us now regard the 

 rectangle ABDC with respect to acceleration tending in the opposite 

 direction. (Sho^vn as line AE, fig. 7.) 



