INSTRUMENTS FOR OBSERVING 25 
especially to meter No. 110 (C. & G. S. No. 172), which is now in the possession of this 
Bureau. The maximum current velocity for which Ekman current meter No. 110 can 
be used successfully is 1.8 knots. Attempts to measure greater velocities with this 
particular meter may result in damage to the instrument. It is recommended that its 
use be limited to velocities of 1.5 knots or less. The instrument is more complicated 
than the Price meter and is designed to indicate both the velocity and direction of the 
current. 
65. In this instrument the meter wheel, which is called the screw, has inclined 
blades after the pattern of a screw propeller, and the number of revolutions is recorded 
on dials in the instrument itself. It is therefore necessary to raise the meter out of the 
water after each observation in order to read the dials. There are two dials which 
FIGURE 17.—Ekman current meter with shutters closed. 
provide for a count up to 4,000 revolutions of the screw. The pointer of the upper dial 
makes one revolution for each hundred revolutions of the screw and the pointer of the 
lower dial makes one revolution for each 4,000 revolutions of the screw. The numbers 
on the dials are in reverse order to give decreasing readings so that the number of revo- 
lutions of the screw in any interval of time may be obtained by subtracting the final 
reading from the initial reading. It will be noted that the numbers inscribed on the 
dials refer to tens of units and require an annexed cipher to give the true number of 
revolutions of the screw. 
66. A locking device is provided to keep the screw from turning when the instru- 
ment is being lowered or raised in the water. The stopper is a small lever inside the 
protecting ring around the screw. It is movable vertically and stops the rotation of 
the screw by coming between the blades. The position of the stopper is controlled by 
