Ocean Temperatures along the West Coast of North America. 257 



of a "bottom-current" of thickness (D) running more or less in the 

 direction of the force, and above this a current reaching right up to 

 the surface with the almost uniform velocity 



gsin* 

 y - " 2w sin* 



perpendicular to the force, where (g) is the acceleration of gravity, and 

 (<i>) is the inclination angle of the surface with a horizontal. In order 

 to represent the result graphically, it is sufficient to so turn (Fig. 5) 

 that the longest arrow points perpendicularly to the left of the pressure 

 gradient. Then add to each arrow in turn the constant velocity (U ) 

 to the right. The successive resultants will be the velocities at the 

 distances 0,0 D, 0,1 D, 0,2 D etc. above the sea bottom. (Fig. 6) has 

 been constructed in this way, (OY) being the direction of the pressure 

 gradient. In the bottom -current the flow in the direction of the 

 pressure gradient is 



10. Sy = 5 = 0,159 U D, 

 while the flow normal to the pressure gradient is 



11. S x = -U D = 



The significance of the above problem may be further brot out by 

 the following explanation. Fluid motion can also be generated by 

 difference in pressure, and in a region of the ocean far removed from 

 obstructions and having a uniform depth greater than (D), it follows 

 from Ekman's theory that if the pressure decreases as shown by the 

 arrow in (Fig. 6) the resulting motion from the upper surface downward 

 to a distance (D) above the bottom will be uniform, tho not in the 

 direction in which the pressure decreases but at right angles to that 

 as shown by the arrow (U ) of (Fig. 6). And the motion between the 

 bottom and a surface at the distance (D) above the bottom can be 

 represented by another spiral stairway, the edge of the top step coin- 

 ciding with (U ) and the successive edges decreasing to zero at the 

 bottom by having the succession of values of the arrows in (Fig. 6). 

 By summing up, as before, the amounts flowing parallel to the pressure 

 gradient and then the amounts normal to the gradient in the different 

 layers of this "bottom stream" it will be found that the total flow or 

 volume per unit time transported in the direction of the gradient is 

 0,159U D while the flow in a perpendicular direction is 0,84 U D. 



1 sideral hour 

 *J 1 pendulum hour = - 



sin* 



