28 MANUAL OF CURRENT OBSERVATIONS 
making one turn for each hundred turns of the screw. Around the circumference of 
the drum there are three pits, each of which, when passing the magazine, carries away 
the lowest ball and, after a-half revolution of the drum,:drops it into the guide tube 
leading to the compass box. Thus there are three balls deposited in the compass 
box for each hundred revolutions of the screw. 
72. Instructions for use.—Because of the complicated construction of the meter 
special care is required in the handling. It should be kept clean and well oiled and 
should be examined frequently to see that all movable parts work freely. Special atten- 
tion must be given to the tubes that convey the direction balls to the compass box, as 
these sometimes become clogged so that the balls cannot pass through. In order to 
clean these tubes it is necessary to remove the gear wheels from the dial box and insert 
a slender wire to free the tubes of any obstruction. 
as 
FiGcurRE 20.—Graduated frame with compass-ball receptacle from Ekman current meter. 
73. When the meter is not in use, the compass needle and the screw should be 
removed from the instrument. Special care must be taken in handling the screw to 
avoid any injury to it. To insert the screw and shaft; release the bar (@), which carries 
the forward bearing, by pushing on the catch (D). Insert the worm end of the shaft 
through the hole in the gear box and secure the bar (@). 
74. To place the needle in the compass box; remove the receptacle (Z) by pressing 
the spring catch on the bottom of the supporting bracket. Remove the compass box 
(Hl) by pressing the catch on the bottom of the frame just above and forward of (#). 
Pry up the cover of the compass box and set the needle on the pivot point. In replac- 
ing the cover, the bevel of the slot for prying off the cover should face downward, and 
the small lug on the box should fit into the small notch on the cover. 
75. A 15-pound streamlined counter-weight preferably of the Colwmbus type should 
be used with the Ekman meter. The small weight supplied with meter No. 110 is 
inadequate. 
76. The vane or tail is attached to the main part of the meter by two brass tubes. 
The tubes are secured to the vane with left-handed screws and are afterwards fastened 
