1. When, after a rather long continuance of fine weather, the barometer
begins to fall in a sudden and continuous manner, rain will certainly
fall; but, if the fine weather has had a long duration, the mercury may
fall two or three days in the tube of the barometer before any change
in the state of the atmosphere may be perceived. Then, the longer the
time between the falling of the mercury and the arrival of the rain,
the longer will be the duration of rainy weather.

2. If, on the contrary, during a rainy period which has already had a
long duration, the barometer commences to rise slowly and regularly,
very certainly fine weather will come, and it will last much longer if
a long interval elapses between its arrival and the rising of the
barometer.

3. In the two cases given, if the change of weather follows immediately
the movement of the barometrical column, that change will last only a
very short time.

4. If the barometer rises with slowness and in a continuous manner for
two or three days, or even more, it announces fine weather, even when
the rain will not cease during those three days, and _vice versa;_ but
if the barometer rises two days or more during the rain, then, the fine
weather having come, if it commences to fall again, the fine weather
will last a very short time, and _vice versa_.

5. In the spring and in the autumn, a sudden fall of the barometer
presages wind. In the summer, if the weather is very warm, it announces
a storm. In winter, after a frost of some duration, a rapid falling of
the barometrical column announces a change of wind, accompanied by a