ch greater pressure
than the mean of the respective localities. With regard to the West
Indian and American hurricanes--any considerable increase of pressure,
especially within the space marked out to the eastward of the 50th
meridian, will demand immediate attention. Upon the barometer ranging
_very high_ within this space, three-hourly observations should be
immediately resorted to; and if possible, _hourly_ readings taken, and
this is the more important the nearer the vessel may be to the 50th
meridian. Each observation of the barometer should be accompanied by an
observation of the wind--its direction should be most carefully noted,
and the force estimated according to the scale in page 21, or by the
anemometer. It would be as well _at the time_ to project the barometric
readings in a curve even of a rough character, that the extent of fall
after the mercury had passed its maximum might be readily discernible by
the eye. A paper ruled in squares, the vertical lines representing the
commencement of hours, and the horizontal tenths of an inch, would be
quite sufficient for this purpose. The _force_ of the wind should be
noted at, or as near to the time of the passage of the maximum as
possible. During the fall of the mercury particular attention should be
paid to the manner in which the wind changes, should any change be
observed; and should the wind continue blowing steadily in _one_
direction, but gradually _increasing_ in force, then such increments of
force should be most carefully noted. During the fall of the barometer,
should the changes of the wind and its increasing force indicate the
neighbourhood of a revolving storm, (independent of the obvious reasons
for avoiding the focus of the storm,) it would contribute as much to
increase our knowledge of these dangerous vortices to keep as near as
possible to their margins as to approach their centres. The recess from
the centre towards the margin of the storm, will probably be rendered
apparent by the _rising_ of the mercury; and so far as the observations
may be considered valuable for elucidating the connexion of atmospheric
waves with rotatory storms (other motives being balanced), it might be
desirable to keep the ship near the margin--provided she is not carried
beyond the influence of the winds which characterize the latter half of
the storm--until the barometer has nearly attained its usual elevation.
By this means some notion might be formed of the general d