each of those great currents, where they strike on the central region of calms. The motion of these great rotatory storms is always in a direction contrary to the sun's apparent daily motion, and therefore, in our hemisphere, contrary to the motion of the hands of a watch, but similar to that motion in the southern hemisphere. The general progress of these storms is always away from the equator, and therefore reversed in the two hemispheres: but in both cases they have first a westward motion, till they escape from the influence of the easterly trade-winds, when they turn round in a hyperbolic curve, and are drifted eastward by the prevailing westerly winds of each temperate zone. Throughout their course they increase in size, till they are lost in the winds of high latitudes, the variable and fluctuating nature of which they greatly increase. "The farther we go from the equator," says Colonel Sir William Reid, "the more complicated this subject becomes; and gales succeed each other so fast during our stormy season, that it is not easy to identify the particular storm we may wish to study. It has been shown that the hurricanes which originate within the tropics increase in diameter and diminish in force as they proceed towards the poles; and as the meridians approach each other, the gales may become huddled together. They may, therefore, frequently neutralise each other, and become irregular.* Their force, too, may often fall off,

* Recent investigation shows that such storms often invade high northern latitudes. In the storm of February 28, 1849, Mr. Milne showed that "its centre passed in a N.E. direction up the Irish Channel and across the south of Scotland; its eastern segment affected severely the south of England, uprooting large trees and causing wrecks, one of which was of an emigrant ship with 160 passengers. Its effects were not so disastrous in Scotland, but its rotatory character was well developed there. At the Observatory on Calton Hill at Edinburgh the gale began with the wind at S.S.E., and it veered round successively to S., S.W., W., and N.W. On the

until the strength of the wind on that side of the circle where it blows from east is unable to reverse the regular westerly atmospheric current, and to convert it into a temporary easterly gale; and this may be a reason why easterly storms are less frequent in both hemispheres in the latitudes within which Great Britain is situated."

Before any rules for the guidance of the navigator can be properly appreciated, it is necessary to gain as precise an idea as possible of the natorm of these great storms, for which purpose the following figure (p. 139) may assist the reader. It is supposed to represent a rotatory storm in the northern hemisphere, revolving in the direction of the curved arrows, while it travels forward in the direction of the large straight arrow, or from E.S.E. to W.N.W.; and if we suppose it to pass over three different ships, situated at different distances from its central track, the effect on them will be the same as if the whirlwind had no progressive motion, and they travelled through it from W.N.W. to E.S.E. along the three dotted lines parallel to the large arrow, but in the opposite direction thereto. By following either of these lines, it will be seen that the wind will blow in succession from the various points marked on each dotted same day it was blowing—at Kinnaird Head and Buchanness from S.E.; at Montrose from S.S.E.; at Edinburgh from S.; in Yorkshire from S.W.; at Pladda lighthouse from W.N.W.; at Corsowall lighthouse from N.W.; at Skerryvore lighthouso from N.; at Glass Island lighthouse from N.E.; at Pentland Skerries lighthouse from E." "There could be no doubt, therefore," adds Mr. Milne, "that this was a whirlwind storm, and that the direction of rotation was from right to left in the northern half of the circle." Sir William Reid also noticed a severe Atlantic storm which passed over the British Islands. It first touched the West coast of Ireland on January 6, 1839, and moved progressively, about E.N.E., over Ireland, the Irish Channel, and Great Britain. It was traced to Gottonburg, in Sweden, and this is the same direction taken by many of the storms which have been traced over North America and the Western Atlantic.

line. For example, the gale experienced by the northernmost ship will begin at E. by N. and veer through six points to S.E. by S. at the end of the storm. The southernmost vessel, being nearer the central track of the storm, will have the wind veering through ten points, beginning at N. by W. and ending at S.W. by W.; while the middle ship, being still nearer the centre of the storm, will have the wind first at N.E., and veering through twelve points until

NNE

NE

it finishes at due South. By observing the distances between the several arrow-heads on either of these lines, especially the last, it will be seen that they thicken towards the middle of the line, showing that the veering of the wind is most gradual on entering and quitting the storm, and most rapid the nearer the centre. But the farther a vessel is from the central track the less will this difference be observed: for example, on the northernmost line, in the figure above, the arrow-heads are more nearly equidistant, showing that the change of

wind is more equable, or nearly as gradual at the middle of the duration of the storm as at its beginning or end.

It will also be observed that the number of points through which the wind veers will be greater the nearer the ship approaches the centre of the storm; but this number can never exceed fifteen, for when a ship is exactly in the central track she will experience no veering, but a constantly increasing gale from one point (in this case N.N.E.), and then a sudden change to the opposite point (S.S.W.); this is a part of very great danger, owing to the sudden change from a violent wind to a perfect calm with a turbulent sea; and the calm have passed onwards with the storm, the ship must be prepared for the equally violent gale to be expected from the opposite point. In approaching this space the mercury in the barometer continually sinks, and rises again in receding from it.

Rules have been drawn up for the use of seamen, to enable them to determine on which tack a ship should be laid-to in any storm of this kind, in either hemisphere and in any part of the world. The object is to prevent the wind from veering by the ship's head, and to insure its veering constantly farther aft, so that she may be constantly coming up to the wind, whereas in the former case she would be breaking off from tho wind, and, even with no sail set, would in so violent a gale be in danger of being driven astern. Colonel Sir William Reid supposed this might have been the cause of many vessels foundering. The avoidance of this danger depends on determining whether the vessel be on the right or left of the central track of the storm. There

* Right and left are here used with reference to the storm's progressive motion, in the same manner as we speak of the right and left banks of a river as we look in the direction in which the water is no ving.

is not much difficulty in determining this point if we observe the manner in which the wind begins to veer; for on referring to figure (p. 139) it will be seen that at all places over which the right-hand half of the storm passes, the wind veers with the sun, or from east to south, or from left to right of the observer, while at all places under the influence of the left-hand semicircle of the storm the wind veers in the contrary direction, or against the sun; and this will be the case in whatever direction the storm may be travelling, and in whichever way it may be rotating; so that in the storms of the Indian Ocean, or in storms of the southern hemisphere, although rotating the contrary way to this, a veering of the wind from the right to the left of the observer will equally indicate that he is at the left side of the storm, and vice versa, although in that hemisphere the expressions" with the sun" and "against the sun" will have their meaning reversed.

Now it has been shown by Colonel Sir William Reid, that in both hemispheres alike, a vessel finding herself at the right side of the storm should be laidto on the starboard tack, and when in its left side on the port tack, to avoid the danger of the wind veering ahead. In this way she will come up to the wind instead of falling off from it. In some cases, however, should the ship forge ahead, she will draw towards the storm's central track. "It may, therefore, be preferable, as a general rule, when heaving-to in a revolving gale, to bring the ship to the wind On the starboard tack when on the north side of the equator, and on the port tack when on the south side of the equator. Then will the ship, when shooting ahead, be gradually moving away from the storm's centre."

It has sometimes been advised that a vessel should always scud before a hurricane. Colonel Sir William