Figures 1 and 2, enlarged and printed on narrow rings of stiff cardboard, are employed for this purpose. The letters outside the thick circle are intended to distinguish the points of the compa.s.s, and in use should always coincide with those points on the chart. The letters within the thick circle indicate the direction of the wind in a hurricane, the whirl being shown by the arrows between the letters. In the northern hemisphere the direction of the whirl is always contrary to that in which the hands of a watch move, and in the southern coincident thereto. The graduation is intended to a.s.sist the mariner in ascertaining the bearing of the centre of a storm from his ship.
_Use._
At any time when a severe gale or hurricane is expected, the seaman should at once find the position of his ship on the chart, and place upon it the graduated point which answers to the direction of the wind at the time, taking care that the needle is directed to the north, so that the exterior letters may point on the chart to the respective points of the compa.s.s: this is very essential. This simple process will at once acquaint the seaman with two important facts relative to the coming hurricane--his position in the storm, and the direction in which it is moving.
_Examples._
A captain of a ship in lat.i.tude 35 24" N., longitude 64 12" W., bound to the United States, observes the barometer to stand unusually high, say 3055 inches: shortly after the mercury begins to fall, at first slowly and steadily; as the gla.s.s falls the wind freshens, and is noticed to blow with increasing force from the S. so as to threaten a gale. The position of the ship on the chart is now to be found, and the graduated point under the letters E. S. is to be placed thereon, taking care to direct the needle to the north. From these two circ.u.mstances, the falling barometer and the wind blowing from the south with increasing force, the mariner is aware of this simple fact, that he is situated in the advancing portion of a body of air which is proceeding towards the N.E.; and if he turn his face to the N.E. he will find he is on the right of the axis line, or line cutting the advancing body transversely. The hurricane circle as it lies on the chart reveals to him another important fact, which is, that if he pursue his course he will sail _towards_ the axis line of the hurricane, and may stand a chance of foundering in its centre. To avoid this he has one of two courses to adopt; either to lay-to on the _starboard tack_, according to Col. Reid"s rules (see his "Law of Storms," 1st edit., pp. 425 to 428), the ship being in the right-hand semicircle of the hurricane, or so to alter his course as to keep without the influence of the storm. In the present case the adoption of the latter alternative would involve a reversal of his former course; nevertheless it is clear the more he bears to the S.E. the less he will experience the violence of the hurricane: should he heave his ship to, upon moving the hurricane circle from the ship"s place on the chart towards the N.E., he will be able to judge of the changes of the wind he is likely to experience: thus it will first veer to S.S.W., the barometer still falling; then to S.W., the barometer at a minimum--this marks the position of the most violent portion of the storm he may be in, and by keeping the barometer as high as he can by bearing towards the S.E., the farther he will be from the centre--the barometer now begins to rise, the wind veering to W.S.W., and the hurricane finally pa.s.ses off with the wind at W. It is to be particularly remarked that in this example the ship is in the _most dangerous quadrant_, as by scudding she would be driven in advance of the track of the storm"s centre, which of course would be approaching her.
a.s.suming that the hurricane sets in at the ship"s place with the wind at S.E., the proceeding will be altogether different. At first the wind is fair for the prosecution of the voyage, and it is desirable to take advantage of this fair wind to avoid as much as possible the track of the centre, which pa.s.ses over the ship"s place in this instance, and is always the most dangerous part of the storm. As the ship is able to make good distance from this track by bearing towards the N.W., provided she has plenty of sea-room, she will experience less of the violence of the hurricane; but as most of the Atlantic storms sweep over the sh.o.r.e, it will be desirable to lay-to at some point on the _larboard tack_, the ship being now in the left-hand semicircle. By moving the circle as before directed it will be seen that the veering of the wind is now E.S.E., E., E.N.E., N.E., the lowest barometer N.N.E., N., and N.N.W., the ship experiencing more or less of these changes as it is nearer to or farther from the axis line.
In lat.i.tudes lower than 20 N. the Atlantic hurricanes usually move towards the N.W. Taking the same positions of our ship with regard to the storms as in the two former examples, if the storm set in with the wind E. the proper proceeding is to bear away for the N.E., the most dangerous quadrant of the hurricane having overtaken the ship, the veering of the wind if she is lying-to will be E., E.S.E., S.E., with the lowest barometer S.S.E. and S. Should the storm set in at N.E., her position at the time will be some indication of the distance of the centre"s track from the nearest land, and will greatly a.s.sist in determining the point at which the captain ought to lay-to after taking advantage of the N.E. wind, should he be able so to do, to bear away from the centre line, so as to avoid as much as possible the violence of the storm. From the proximity of the West Indian Islands to this locality of the storm-paths, the danger is proportionally increased.
The above examples have reference only to the lower and upper branches of the storm paths of the Northern Atlantic in the neighbourhood of the West Indies and the United States. In lat.i.tudes from about 25 to 32 these paths usually _re-curve_, and at some point will move towards the north. The veering of the wind will consequently be more or less complicated according as the ship may be nearer to or farther from the centre. The tables on page 11, combined with the first of those immediately following the next paragraph, will, it is hoped, prove advantageous in a.s.sisting the mariner as to the course to be adopted. As a general principle we should say it would be best to bear to the eastward, so as not only to avoid the greater fury of the storm, but to get into the S. and S.W. winds, which give the princ.i.p.al chances of making a westerly course.
We have in page 44 called attention to the fact that the storm paths traced by Mr. Redfield do not extend eastward of the 50th meridian. This by no means precludes the existence of severe storms and those of a rotatory character in the great basin of the Northern Atlantic, especially between the 40th and 50th parallels. A remarkable instance has come under the author"s attention of the wind hauling _apparently_ contrary to the usual theory: it may be that the storm route was in a direction not generally observed. We are at the present moment dest.i.tute of any information that at all indicates a _reversion_ of the rotation in either hemisphere. The following tables constructed for the northern hemisphere, and for storm routes _not yet ascertained_, may probably be consulted with advantage on anomalous occasions.
HURRICANE MOVING FROM SOUTH TO NORTH.
Axis line, wind E., barometer falling, first half of storm.
Axis line, wind W., barometer rising, last half of storm.
RIGHT-HAND SEMICIRCLE.
Wind E.S.E., S.E., S.S.E., S., barometer falling, first half of storm.
Wind W.S.W., S.W., S.S.W., S., barometer rising, last half of storm.
LEFT-HAND SEMICIRCLE.
Wind E.N.E., N.E., N.N.E., N., barometer falling, first half of storm.
Wind W.N.W., N.W., N.N.W., N., barometer rising, last half of storm.
HURRICANE MOVING FROM NORTH TO SOUTH.
Axis line, wind W., barometer falling, first half of storm.
Axis line, wind E., barometer rising, last half of storm.
RIGHT-HAND SEMICIRCLE.
Wind W.N.W., N.W., N.N.W., N., barometer falling, first half of storm.
Wind E.N.E., N.E., N.N.E., N., barometer rising, last half of storm.
LEFT-HAND SEMICIRCLE.
Wind W.S.W., S.W., S.S.W., S., barometer falling, first half of storm.
Wind E.S.E., S.E., S.S.E., S,, barometer rising, last half of storm.
HURRICANE MOVING PROM WEST TO EAST.
Axis line, wind S., barometer falling, first half of storm.
Axis line, wind N., barometer rising, last half of storm.
RIGHT-HAND SEMICIRCLE.
Wind S.S.W., S.W., W.S.W., W., barometer falling, first half of storm.
Wind N.N.W., N.W., W.N.W., W., barometer rising, last half of storm.
LEFT-HAND SEMICIRCLE.
Wind S.S.E., S.E., E.S.E., E., barometer falling, first half of storm.
Wind N.N.E., N.E., E.N.E., E., barometer rising, last half of storm.
HURRICANE MOVING FROM NORTH-WEST TO SOUTH-EAST.
Axis line, wind S.W., barometer falling, first half of storm.
Axis line, wind N.E., barometer rising, last half of storm.
RIGHT-HAND SEMICIRCLE.
Wind W.S.W., W., W.N.W., N.W., barometer falling, first half of storm.
Wind N.N.E., N., N.N.W., N.W., barometer rising, last half of storm.
LEFT-HAND SEMICIRCLE.
Wind S.S.W., S., S.S.E., S.E., barometer falling, first half of storm.
Wind E.N.E., E., E.S.E., S.E., barometer rising, last half of storm.