is known to sailors as the 'doldrums' and many a
sailing-vessel has been held for weeks there, without enough wind to
carry her the few miles necessary to get into the next belt of winds;
outside this, come the downflowing easterly currents, known as the trade
winds, which form a belt between the tropics and the temperate zones.
Beyond this--to the north and south of the tropical zones--come the
prevailing belts of strong west winds, which stretch almost to the
Poles.

"The United States is in this west-wind zone and the strength and
regularity of the eastward movement of the weather is because both the
winds of the surface and of the upper air blow in the same direction.
Naturally, the same conditions are repeated on the other side of the
equator. In the southern hemisphere the land masses are not so large and
the regularity of the winds is less disturbed. There, the west winds are
so strong that certain latitudes are known as the 'roaring forties.'
These 'forties' correspond in latitude to the northern third of the
United States. Chicago and New York are both in the 'roaring forties' of
the northern hemisphere."

"The way you tell it, it sounds all right," the farmer objected, "but
from my experience, winds blow from all over the place."

"Locally, perhaps, they seem to," the weather expert responded, "but if
you watched them closely, you'd find that about seventy per cent of the
winds come from a westerly direction."

"They do here, for a fact," put in Tom, who, as official wind-measurer
of the League, had been following the explanation with the keenest
attention. "I've noticed that in my kite-flying. The winds are from the
southwest or from the northwest nearly all the time."

"You mean both in summer and winter?"

"Yes," answered Tom, "they're more from the northwest in winter, I
think, but they're generally westerly."

"If the winds are due to the position of the equator and the poles," the
old farmer said shrewdly, "I don't see why summer and winter ought to
make any difference."

"That," said the Forecaster, "is due to an entirely different set of
conditions. It's due to the difference in radiation. There's much
greater change in temperature over the land than over the sea. Take an
island like Bermuda, for example. From the hottest day in summer to the
coldest day in winter there isn't a change of more than forty degrees,
because Bermuda is surrounded by water and is near warm ocean currents.
In Arizon