20 MANUAL OF CURRENT OBSERVATIONS 
shaft contact a wire spring similar to the one used for the single-count device. One 
of these contacts is made for every 5 revolutions of the cup shaft. The eccentric and 
worm gear are both on the cup shaft, the eccentric being above the worm gear. The 
contact chamber is provided with two contact plugs, each with a wire contact spring. 
The upper spring contacts the eccentric for the single-count operation and the lower 
spring contacts the projections on the gear-wheel shaft for the penta-count operation. 
Hither device is made operative as desired by connecting the proper plug with one of 
the wires of the electric circuit of the registering device. The other wire is grounded 
to the supporting yoke of the instrument. 
50. The meter is provided with two tail vanes set at right angles, one in a horizontal 
plane and the other in a vertical plane. The vanes may be separated when the instru- 
ment is dismantled for packing. The vanes with their stem balance the head and also 
keep the axis of the meter parallel to the direction of the current. On one of the vanes 
there is a slot carrying a weight that can be adjusted to balance the meter. The meter 
is supported by a flat rod or stem that passes through a slot in the yoke and is secured 
by a bolt which permits some movement in a vertical plane so that the axis of the meter 
may retain a direction parallel to the direction of the current, although the supporting 
stem itself may be carried out of the vertical by the force of the current against the 
instrument asa whole. Attached to the lower end of the supporting stem is a torpedo- 
shaped weight to assist in holding the instrument at a desired depth. At the upper 
end of the stem is an arrangement for attaching a cable. 
51. When in use the meter is supported by a cable containing 3 insulated wires. 
One of these is a stranded steel wire designed to support the instrument and attached 
weight. The other two are copper wires used to complete an electric circuit between 
the instrument and an earphone used by the observer. A small battery is connected 
in the circuit, and when this circuit is made and broken by the revolution of the meter 
wheel, audible clicks in the earphone can be counted by an observer. 
52. Installation of meter.—In taking meter observations from a boat, a beam is 
rigged outboard so that when the apparatus is raised or lowered it will clear the side 
of the vessel. As it is the usual practice to take observations at several depths at the 
same station, frequent changes in the height of the instrument are necessary. To 
accomplish this conveniently it has been found advantageous to suspend the meter from 
a cable which is reeled on the drum of a hand-sounding machine. The end of the current 
cable is passed through a hole drilled through the face of the sounding-machine drum 
to a connecting plug which is made fast in one of the holes in the web of the reel. The 
reel may be rotated to raise or lower the meter, and when it is at the deswed depth the 
earphone and battery are plugged in, thus completing the electric circuit. 
53. Since in strong currents there is a tendency for the meter and current cable 
to trail out or depart from a vertical line, it has been found desirable to have the meter 
slide up and down a second cable that is held vertically by a 200-pound weight attached 
to its extremity (fig. 15). The weight is raised or lowered by means of a small hand 
winch. After the weight has been lowered to a depth below the lowest point at which 
observations are to be taken at the station, it may be left in this position until all the 
observations at the station have been completed. Shackles are used to hold the 
meter close to the cable supporting the heavy weight. The meter itself may then be 
raised or lowered as desired without changing the position of the large weight. The 
current cable and the cable supporting the weight pass over separate sheaves fastened 
to the beam supporting the apparatus. The sheave through which the current cable 
passes may contain a registering dial to show the depth to which the meter is lowered. 
