INSTRUMENTS FOR OBSERVING 27 
the action of springs, and also releases the stopper and permits the screw to rotate with 
the current. 
68. The second device for stopping the rotation of the screw, for use at the con- 
clusion of the measurement of the current, is a twin-spring lever (/”) extending upward 
near the inner end of the locking lever. When the latter receives a blow from a second 
messenger (NV) dropped by the observer, it is forced down and caught by the twin- 
spring lever which holds it in the locked position until the meter is raised to the surface. 
When the meter is being set preparatory to taking an observation, the twin-spring lever 
must be pressed toward the supporting cable and secured by the ratchet (B) so that it 
will remain inoperative until after the first messenger has been dropped. The first 
messenger releases the ratchet and permits this lever to resume its normal position 
ready to function as soon as the second messenger is dropped. ‘The messengers weigh 
approximately one-half pound each and are designed so that they can be readily attached 
to the cable on which they slide freely. 
69. For obtaining the direction of the current, the meter is provided with a com- 
pass needle (fig. 19) of magnetized rods which carries a small chute or grooved arm 
extending from the center to the south end of the needle. From a guide tube above the 
center of the needle small bronze balls are dropped one at a time and roll along the 
FIGURE 19.—Compass needle of Ekman current meter. 
chute until they drop off at the south end. In the bottom of the compass box (A) 
there are 36 holes separated by radial partitions and below this compass box there is a 
receptacle (Z) containing 36 compartments corresponding to the 36 holes above. As 
the meter swings with the changing direction of the current, different compartments 
of the receptacle are brought under the south end of the compass chute, and the par- 
ticular compartment into which any ball rolls will indicate the direction of the current 
at that time. 
70. Hach compartment represents 10° of azimuth. The zero or north compart- 
ment, which is distinguished by being colored red, provides for an arc extending from 
5° west of north to 5° east of north; and when the receptacle is fitted into the meter, 
this compartment is on the side furthest from the vane of the instrument. The com- 
partments themselves are not marked by numbers. After the meter is taken from the 
water, the receptacle is removed from the instrument and placed in a circular graduated 
frame (fig. 20) with divisions numbered counterclockwise from 0 to 35. When fitted 
in the frame the red or north compartment of the receptacle is adjacent to the 0 gradua- 
tion of the frame. A ball in any compartment then indicates a current-having an 
approximate azimuth corresponding to the number on the frame with a cipher annexed. 
For example, a ball in compartment No. 1 indicates a current flowing approximately 
N. 10° E., or between the limits N. 5° E. and 15° EK. A ballin compartment No. 35 
indicates a current flowing approximately N. 10° W. 
71. The bronze balls are kept in a magazine consisting of a tube (Z) which leads 
to a drum in the gear box of the instrument. This drum rotates as the meter operates, 
878447°—50—_3 
