be renewed;
and the shifting of the wind towards the N.W. will be indicated by a
fall of the thermometer as well as a rise of the barometer.

Three things appear to affect the mercury in a barometer:--

1. The direction of the wind--the North-east wind tending to raise it
most--the South-west to lower it the most, and wind from points of the
compass between them proportionally as they are nearer one or the other
extreme point.

N.E. and S.W. may therefore be called the wind's extreme bearings
(rather than _poles_?)

The range, or difference of height, of the mercury, due to change of
direction _only_, from one of these bearings to the other (supposing
strength or force, and moisture, to remain the same) amounts in these
latitudes to about half an inch (shown by the barometer as read off).

2. The amount, taken by itself, of vapour, moisture, wet, rain, hail, or
snow, in the wind or current of air (direction and strength remaining
the same) seems to cause a change amounting, in an extreme case, to
about half an inch.

3. The strength or force alone of wind from any quarter (moisture and
direction being unchanged) is preceded, or foretold, by a fall or rise,
according as the strength will be greater or less, ranging, in an
extreme case, to more than two inches.

Hence, supposing the three causes to act together--in extreme cases--the
mercury might range from about 31 (30.9) inches to near 27 inches, which
has happened _occasionally_.

Generally, however, as the three act much less strongly, and are less in
accord--ordinary varieties of weather (the wind varying as usual--with
more or less cloudiness, or rain) occur much more frequently than
extreme changes.

Another general rule requires attention; which is, that the wind usually
veers, shifts, or goes round, _with the sun_, (right-handed in northern
places, left-handed in the southern parts of the world,) and that, when
it does not do so, or backs, more wind or bad weather may be expected
instead of improvement.

In a barometer the mercury begins to rise occasionally before the
conclusion of gale, sometimes even at its commencement, as the
equilibrium of the atmosphere begins to be restored. Although the
mercury falls lowest before high winds, it frequently sinks considerably
before heavy rain only. The barometer falls, but _not always_, on the
approach of thunder and lightning, or when the atmosphere is highly
charged with electricity.[16] Before and durin