U. S. DEPARTMENT OF AGRICULTURE WEATHER BUREAU. EXPLANATION OF FLAG SIGNALS,
[Illustration: Flags]
No. 1, alone, indicates fair weather, stationary temperature.
No. 2, alone. Indicates rain or snow, stationary temperature.
No. 3, alone, indicates local rain, stationary temperature.
No. 1, with No. 4 above it, indicates fair weather, warmer
No. 1, with No. 4 below it, indicates fair weather, colder.
No. 2, with No. 4 above it, indicates warmer weather, rain or snow.
No. 2, with No. 4 below it, indicates colder weather, rain or snow.
No. 8, with No. 4 above it, indicates warmer weather with local rains.
No. 3, with No. 4 below it, indicates colder weather with local rains.
No. 1, with No. 5 above it, indicates fair weather, cold wave.
No. 2, with No. 5 above it, indicates wet weather, cold wave.
Forecasts made at 10 A.M., and displayed between 12 and 1 P.M., forecast the weather for the following day until 8 P.M.
FORECASTING THE WEATHER 245
Plant Barometers
The dandelion is an excellent barometer, one of the commonest and most reliable. It is when the blooms have seeded and are in the fluffy, feathery condition that its weather prophet facilities come to the fore. In fine weather the ball extends to the full, but when rain approaches, it shuts like an umbrella. If the weather is inclined to be showery it keeps shut all the time, only opening when the danger from the wet is past.
The ordinary clover and all its varieties, including the trefoil and the shamrock, are barometers. When rain is coming, the leaves shut together like the shells of an oyster and do not open again until fine weather is assured. For a day or two before rain comes their stems swell to an appreciable extent and stiffen so that the leaves are borne more upright than usual. This stem swelling when rain is expected is a feature of many towering grasses.
The fingers of which the leaves of the horse chestnut are made up keep flat and fanlike so long as fine weather is likely to continue. With the coming of rain, however, they droop, as if to offer less resistance to the weather. The scarlet pimpernel, nicknamed the "poor man's weather glass," or wind cope, opens its flowers only to fine weather. As soon as rain is in the air it shuts up and remains closed until the shower or storm is over.