26 MANUAL OF CURRENT OBSERVATIONS 
FIGURE 18.—Ekman current meter with shutters open. 
the position of the locking lever (CQ) which is movable vertically on a bearing at the 
top of the instrument. There are two separate devices for holding the locking lever 
in the position necessary to keep the screw from turning. 
67. The first device for holding the locking lever is used in setting the instrument 
before lowering it into the water for an observation, and consists of placing the outer 
end of the lever (A) against the upper edge of the upper shutter in front of the protecting 
ring around the screw, the two shutters being first closed. After the instrument is 
lowered into the water, this device is released by letting a weight, known as the messen- 
ger (M4), slide down the supporting cable. When the messenger strikes the inner end 
of the locking lever, the latter releases the shutters which automatically fly open by 
