22 
where ¢ is the projection on the sea surface, and ¢ is the geographical 
latitude. Substituting this new value for = we have 
Sop SID et ee 2c ee 
but Hii 'B'D!'' C'' = (¢— cy) ,L where 
¢) =velocity per second in a given horizontal plane. 
c, =velocity per second in another horizontal plane. 
L =distance between stations. 
Substituting in (d) for the new value = we have 
Qe \sinig' (Coe) Leet 2 eee) 
STATION «A. “ 
Co-C, 
‘ 
Fic. 6.—Lines AA’ and BB’ represent the velocity of the surface current, or co, per unit T; CC’ 
and DD’ indicate the velocity of the current at a greater depth, or c1. The difference in the 
velocity of the two movements is equal to D’”” B’, or co—c1. The movement is assumed to be 
normal to the vertical plane ABDC, which is passed through the two stations A and B. Area 
OC” D” B’ A’, indicated by the symbol c, represents the difference in the change of areas per 
change of T, projected on the sea surface and developed by the progression of the two lines AB 
and CD with the respective velocities co and 
Thus by (e) we are furnished with an expression for the effect of 
terrestial rotation in terms of the latitude; the distance between 
stations; and the difference in velocity of the current between any 
two levels. It is easy to see that if we are able to find some point along 
the verticals where zero velocity prevails, then we have a means of 
expressing the real velocity. It is customary to extend the investi- 
gations to depths where it is believed motionless water lies, and then 
¢:=0, and ¢ is the true velocity on the surface. (See p. 13 regarding 
the obliquity of isobaric surfaces.) 
