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6 TECal\f1QUES OF WATER-RESOURCES INVESTIGATIONS ~- ; i in shallow depths. (See fig. 4.) The pygmy meter is scaled two-fifths as large as the stand- ard meter and has neither a tailpiece nor a pentagear. The contact chamber is an integral part of the yoke of the meter. The pygmy meter makes one contact each revolution and is used only for rod suspension. The Geological Survey has recently developed a four-vane vertical-axis meter. (See fig. 5.) This meter is useful for measurements under ice cover because the vanes are less likely to fill with slush ice, and because it requires a much smaller hole to pass through the ice. One yoke of the vane meter is made to be suspended at the end of a rod and will fit holes made by an ice drill. Another yoke is made for regular sus- pensions. (See fig. 5.) The vane meter has a disadvantage of not responding as well as the Price type AA meter at velocities below 0.5 fps. A new contact chamber has been designed by the Geological Survey to replace the wiper Figure 5 -Vane ice meter, top; and vane meter with cable suspension yoke, bottom. contact of the type AA and vane meters. The new contact chamber contains a magnetic switch, glllSS enelosed in a hydrogen atmosphere and hermetically sealed. The switch assembly is rigidly fixed in the top of the meter head just above the tip of the shaft. The switch is operated by a small permanent magnet rigidly fastened to the shaft. The switch quickly closes when the magnet is alined with it, and then promptly operis when the magnet moves away. The magnet is properly balanced on the shaft. Any type AA meter can have a magnetic switch added by replacing the shaft and the contact chamber. (See fig. 6.) The magnetic switch is placed in the special contact chamber through the tapped hole for the binding post. The rating of the meter is not altered by the change. An automatic counter (see p. 31) is used with the magnetic-switch contact chamber. If a head- phone is used, arcing can weld the contacts. A Price meter accessory that indicates the direction of flow is described on page 27. II Figure 6 -Ma9netic switch contact chamber, sheft, and adapter bushing, lefti and cat's whisker contact chamber and shaft, right.