an extensive region, revolving
horizontally--or inclined at a certain angle to the horizontal plane.

If the observer be stationary, in North latitude, and the centre pass on
his polar side, he will experience a change of wind from Southward by
the West towards North; but if it pass between him and the Equator, the
change will be from Southward by the East towards North; but otherwise
in South latitude, as his place in circles sketched will show more
clearly than words. The roughest sketch or diagram, indicating the
various directions of wind, and the course of the meteor's centre, will
show more plainly than descriptions--which must necessarily vary with
each case, and are tedious.

Cyclonology, or really meteorology, is simple enough in these great
characteristic effects; but their causes must be the philosopher's
study, rather than that of the young practical seaman.

Were it not for this reflection, one might endeavour to show how all the
great Easterly trade winds--the no less important anti-trades,[29] or
nearly constant Westerly winds,--and their complicated eddying offsets,
are all (on greater or smaller scales) breadths, or zones of atmosphere,
alternating, or circulating, or crossing (superposed or
laterally)--between which, at distant intervals, occur those strong
eddies, or storms, called hurricanes--typhoons--tornadoes--or cyclones.

The great easterly and westerly movements--so clearly shown by
philosophers to be the consequences of cold polar currents of air--warm
equatorial currents--and diurnal rotation of the earth;[30] are grand
ruling phenomena of meteorology--to which storms, and all local changes,
occurring but occasionally, are subordinate and exceptional. Further
investigations into electrical and chemical peculiarities will probably
throw additional light, perhaps the strongest, on meteorological
science.

* * * * *

In the previous observations, general reference has been made to
mercurial barometers of the ordinary kind; but, excepting the
construction of the instruments themselves, those observations apply to
all barometers, wheel--aneroid--or metallic--and likewise, of course, to
the sympiesometer, which is a modified barometer. But as these four
last-mentioned instruments are scarcely so familiar as the simplest form
of barometer, it may be useful to add a few words about each of them.

* * *

The WHEEL barometer has a syphon tube,