her exceptional phenomena and not thoroughly understood. The winds
seem to blow in from all directions toward an area of very low pressure
at a single point. The spiral motion that is common to all cyclones, in
a tornado seems to be gathered up into a condensed form, like a funnel.
The direction of movement is the same as that of the cyclone--that is,
in the reverse direction to that of the hands of a watch. The upward
motion of the air inside of the funnel is at a rate of over 170 miles an
hour. The onward movement of the whole system is about thirty miles per
hour.

Tornadoes occur with greater frequency in the United States than in any
other section of the globe. Tornadoes seldom occur in winter, except
perhaps in the Southern States. They are more frequent in the month of
May than at any other time during the year, although they occur
sometimes in April, June, and July.

Between 1870 and 1890 about sixty-five destructive tornadoes occurred in
the United States, involving great loss of life and property. When a
tornado moves off the land on to the ocean it may become what is termed
a waterspout. These probably never originate on the water, but after
they have once formed may be carried over the water to a considerable
distance. A tornado was never known to originate on the shores of Lake
Michigan, but there are a few instances (the most notable one being the
Racine tornado) when they have reached the lake after having traveled
from some distant point inland.

The Racine tornado--so called because it destroyed a large portion of
that city--happened fifteen or more years ago. The tornado originated
about 100 miles southwest of Racine, Wis., in northern Illinois. The
funnel-shaped cloud passed over the lake, but the tornado character of
the storm was broken up before it reached the other shore.

When a tornado passes from land to water it becomes a waterspout only
when the cloud-funnel hangs low enough and the gyratory energy is
sufficiently great. There is a great pressure on the water outside of
the funnel and almost a perfect vacuum inside. This latter fact
contributes largely to the destructive power of the tornado. When a
funnel is central over a building a sudden vacuum is created outside of
it and it bursts outwardly from the internal air pressure.

CHAPTER XIII.

WEATHER PREDICTIONS.

To predict with any great accuracy what the weather will be from day to
day is a somewhat complicated problem, an