barometer and vane.
The usual indications of a storm in connexion with these instruments are
the _falling_ of the barometer and the _freshening_ of the wind, and it
is generally considered that a _rapid_ fall of the mercury in the
hurricane regions invariably precedes the setting in of a storm.

There are three classes of phaenomena that present themselves to an
observer, according as he is situated _on_ the line or axis of
translation, or _in_ either the right or left hand semicircle of the
storm. These will be rendered very apparent by a little attention to the
annexed engraving, fig. 1.

[Illustration: Compass rose]

In this figure the arrow-head is supposed to be directed true north, and
the hurricane--as is the case in the American storms north of the 30th
parallel--to be moving towards the N.E. on the line N.E.--S.W. If the
ship take the hurricane with the wind S.E.,--the letters within the two
larger circles indicating _the direction of the wind in the storm_
according to the rotation as shown by the circle of arrow-heads, and
which it is to be particularly noted is in the northern hemisphere
_contrary to the direction in which the hands of a watch move_: in the
southern hemisphere the rotation is reversed--the only phaenomena
presented by the storm are as follows:--The wind continues to blow from
the S.E., increasing considerably in force with the barometer falling to
a very great extent until the centre of the storm reaches the ship, when
the fury of the winds is hushed, and a lull or calm takes place,
generally for about half an hour, after which the wind springs up mostly
with increased violence, but from the opposite quarter N.W., the
barometer begins to rise, and as the storm passes off, the force of the
wind abates.

The point to which we wish particularly to direct attention in connexion
with this exposition of the phaenomena attending the transmission of a
storm is this:--If the observer so place himself at the commencement
that the wind passes _from his left hand towards his right_, his face
will be directed towards the centre of the storm; and the wind
undergoing no change in direction, but only in force, will acquaint him
with this important fact that the _centre_ is not only gradually but
surely approaching him: in other words, in the case before us, when he
finds the wind from the S.E., and he places himself with his face to the
S.W. he is looking towards the centre, and the wind rushes past him