Man's physical universe

xanabras

266 PHYSICAL LIMITATIONS HAVE BEEN OVERCOME

San Francisco, Jacksonville, Kansas City, and Washington, U. C, at

each of which they are charted and forecasts made for that district

from the charts. Reports are also received from ships at sea, and

other reports are interchanged with Mexico and Canada.

At headquarters highly trained men receive and decode the messages.

They then chart this information.

The next step is a physical interpretation of the present state of the

weather. On the basis of these conclusions and past experience, the

Fig. 86. The aneroid barograph. (Courtesy of the U. S. Weather Bureau.)

weather to be expected for the next twenty-four to thirty-six hours is

forecast.

The forecasts of

the Weather Bureau are widely distributed from

different district headquarters by telegraph, mail, and telephone; the

newspapers, radio short wave, and the teletype telegraph machine are

also widely used to broadcast coming weather conditions.

Cyclones and Anticyclones Are Charted in Weather-forecasting.

Areas of relatively high barometric pressure, called "anticyclones,"

and areas of relatively low pressure, called "cyclones," pass over the

United States from westerly toward easterly directions, in succession,

with speeds varying from about twenty miles per hour in the summer

to thirty miles per hour or more in the winter. These so-called highs

and lows cover territories ranging up to more than a thousand miles

in diameter. Highs generally are accompanied by fair weather, though

not always, whereas lows usually represent more or less stormy con-

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