CHAP. XIX.] DEEP-SEA CURRENT METER 415 



E E are four small cones, which revolve on their axis in a 

 vertical plane similar to an anemometer. The axis is con- 

 nected by a worm-screw to geared wheels, which register the 

 number of revolutions up to 5,000, corresponding to about four 

 nautical miles. There is a small lever in connection with A A 

 which prevents the cones from revolving when the machine is 

 locked, but allows them to revolve freely when the meter is in 

 action. Below the rudder-post is a compass-bowl F, which is 

 hung in gimbals, and capable of removal. The needle is so 

 arranged that it can be lifted off the pivot by means of a lever 

 in connection with A A. When the meter is in action the 

 needle swings freely on its pivot, but when the levers are locked 

 it is raised off its pivot by the inverted cup-piece K placed 

 inside the triple claws on the top of the compass, and screwed 

 to the lever, thus locking the needle without chance of moving. 

 The compass-bowl should be filled with fresh water before 

 lowering the instrument into the sea, and the top screwed home 

 tightly. The needle should be removed and carefully dried 

 after use, to prevent corrosion. The long arm G is to keep the 

 machine steady in one direction. It works up and down a 

 jackstay, which passes between two sheaves at the extremity 

 of the long arm. This also assists to keep the machine in as 

 upright a position as possible, and prevents it from being 

 drifted astern with the current. A weight of as much as 8 or 

 10 hundredweight is required at the bottom of the jackstay 

 in a very strong current. An elongated weight of from 60 to 

 80 pounds must be suspended from the eye at the bottom of 

 the meter to help to keep it as vertical as possible. On the 

 outer part of the horizontal notched ring forming the frame, 

 and placed on the side of the machine opposite to the projecting 

 arm G, it has been found necessary to bolt a short arm supported 

 by stays from above, from which is suspended a leaden counter- 

 poise weight to assist in keeping the apparatus upright. This 

 additional fitting is not shown in Fig. 86. A three-quarter-inch 

 phosphor-bronze wire rope is used for lowering the machine. It 

 is rove through a metal sheave H and india-rubber washer, and 

 spliced round a heart which is attached to the metal plate B. 

 The messengers are fitted with a hinged joint to enable them 

 to be placed round the wire rope, and secured with a screw bolt. 

 To obtain the exact value of a revolution of the small cones, 



