846 EIGHTH PACIFIC SCIENCE CONGRESS 



trodes, i.e. the latter is 100 m. distant from the former. Then they are 

 driven into sea and the cord is tied to the ship as the shorter electrode 

 stays about 100 m. from the stern of the ship. 



These works are conducted when the ship is running. WTien all 

 have been prepared well, measurements are begun. 



At first and at last, the zero point confirmed by the longer cord 

 is shortened till the length becomes the same as that of the shorter one, 

 i.e. the two electrodes lie side by side. We got the constancy of the 

 zero point in the range of 0.2 mV or less, which corresponds to about 

 0.1 kt of the current velocity. 



After confirmation of zero point, we prolong the longer cord to 

 full length. Then the meter indicates some millivolt, which shows 

 the e.m.f. produced by the component of the ocean current perpendi- 

 cular to the direction of the ship course. Then we turn the course to 

 another direction, preferably near right angle. When the needle of 

 the meter sets in the new direction, it indicates the e.m.f. of the com- 

 ponent perpendicular to the new direction. Under the assumption that 

 the current is constant during the turning of direction, or the two com- 

 ponents can be considered to be those of the same vector of the current 

 velocity, we can compose the total velocity from the two components of 

 velocity and the direction of the course of the ship, which is known by 

 the compass. 



The composition of these vectors is, ho^\'ever, a little different from 

 the ordinary method. We draw the respective vectors of the compo- 

 nents, from the same point in the middle of turning. The scalor 

 amount is given from the reading of the potentiometer and the direc- 

 tion must have been informed from the bridge of the ship, whenever 

 the reading is taken. Then, the intersection of the two perpendiculars 

 from the respective points of the component vectors must be the top of 

 the composed vector, drawn from the same origin. 



In such a way, we can measure easily the vectorial velocity of the 

 ocean current from the moving ship. For the check of these values, we 

 compared the values of the amount of the drift of a ship by the cur- 

 rent measured by our method and by calculatiou from the positions 

 of the ship at the beginning and the end. The position of the ship 

 was confirmed by triangular survey by a sextant. 



(3) Practical Measurement of Ocean Current 

 1. Off the point Nojima-zaki. 



Nojima-zaki is situated at the south edge of the Bohsoh Peninsula, 

 Clhiba prefecture, Japan. The warm current "Kuroshio" flows along 



