Pacific and High Southern Latitudes. 109 
One swell therefore precedes, and an opposite swell succeeds, 
a hurricane: these swells will be greater than any other. 
The swelis of oblique directions intersect and form a “heavy 
cross sea.” As they all necessarily intersect at the centre, 
their super-position raises there confused pyramidal seas, 
having extreme vertical, but little lateral, motion. 
This coincidence of swells at the centre I conceive to be 
the true cause of the strange seas always met with there, 
although all writers agree in ascribing them to the dimimished 
atmospheric pressure, which will only produce a general 
elevation of the surface of about two feet, and will not 
account for the great vertical oscillations of the central 
waves. ‘he dense air near the circumference of the storm 
has a retarded circular motion; and from the tendency of 
each revolving particle of air to obey the dynamical law of 
the conservation of areas, the wind blows stronger and 
stronger as we approach the axis: but in the immediate 
neighbourhood of the centre there exists a perfect calm, the 
¢ 
sky overhead is clear, forming what is called the “ eye’ of 
the storm; while a dense bank of clouds rests all around the 
horizon. A 
In the Southern Hemisphere the circular motion of the 
wind is the same in direction as that of the hands of a watch; 
and in the opposite direction in the Northern Hemisphere. 
The whole storm moves bodily across the ocean; but the 
rotatory motion is much more violent than the progressive, 
and constitutes the ‘“‘ gale’ of seamen. 
Tropical storms begin near the equator, move from it to 
the westward, recurve, and pass to the eastward into middle 
latitudes. 
The circumstances of the formation and final extinction of 
whirlwind storms are unknown; but many reasons lead me to 
