Man's physical universe

xanabras

WEATHER-FORECASTING 265

The cup anemometer measures the velocity of the wind and records it

by means of an electrical-contact system. Dials geared to the shaft

read miles per hour directly, while automatic

records are made on a time graph

in the station every time a mile of wind

passes the station. The wind direction is

recorded every minute by an electrical

connection to the weather vane and is

registered on the same graph.

The rain gauge and the sunshine

recorder are also provided with electric

devices that make it possible to register

the amount of precipitation and sunlight

on the same graph. The sunshine recorder

consists of two bulbs connected

Fig. 84. Robinson four-cup

anemometer with cups attached

by a narrow glass tube which extends

and dial cover off. (Courtesy of

down into the lower bulb. The lower the U. S. Weather Bureau.)

bulb is covered with lampblack and is

partially filled with mercury. The lampblack absorbs heat and thus

expands the air within this bulb, forcing the mercury up into the small

Fig. 85. The sunshine recorder.

(Courtesy of the U. S. Weather Bureau.)

tube, sealed at one end and inverted

into the mercury. The mercury in

the tube closes electrical contacts

as long as the sun is shining. The

outer tube is evacuated to prevent

loss of heat by conduction. The

self-recording rain gauge operates

by a tiny bucket that tips each time

a hundredth of an inch of rain has

fallen into it,

thus making an electrical

contact that operates the

recording pen.

Twice each day nearly three hundred

skilled weather observers in

the United States, Alaska, and the

West Indies telegraph their local

observations in code to the district

headquarters — at 8 a.m. and

8 P.M., E.S.T. Observations of the

temperature, barometric pressure,

direction and velocity of wind, and the precipitation are telegraphed

to these district forecasting stations at Chicago, New Orleans, Denver,

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