350 



HYDRAULICS AND ITS APPLICATIONS 



plane, and the change in this relation with any change in the state of 



a river. 



ART. 99. CURRENT METERS. 

 Meters in use at the present day may be divided into two classes . 



(1) those in which the revolving part carries a series of helicoidal vanes 



mounted on a horizontal 

 axis, and (2) those in 

 which a series of conical 

 or hemispherical cups is 

 mounted on arms, as in 

 an anemometer, on a 

 vertical axis. The former 

 type is illustrated in Fig. 



154, which shows the 

 Amsler meter and in Fig. 



155, which shows the 

 Haskell meter, while the 



latter is shown in Fig. 156, which illustrates the Price meter. The latter 

 type of meter has some advantages over the former in that friction is 

 usually less since it practically all comes on one point which is easily 

 protected from any grit in the water, while in addition this type will start 

 in a current of less velocity than will move the other, and yet will not 

 revolve as rapidly under the same conditions of high velocity flow. 



The meter is fitted with a guide vane which keeps its axis perpen- 

 dicular to the direction of the current. The wheel may be either geared 

 to a counter which records the revolutions direct and is put into and out 



FlG. 154. Amsler Current Meter. 



FIG. 155. Haskell Current Meter. 



of gear by means of a cord from the point of suspension of the meter, or 

 mi y make and break the contact in an electrical circuit at each revolu- 

 ti n, thus enabling the number of revolutions to be indicated by means 

 oi a counter or buzzer placed on shore or in a boat. The advantages of 

 the latter method in reducing the resistance to rotation and the tendency 



