as much as two inches, thus diminishing the atmospheric pressure by th part. As a consequence of this, cold air is brought down from the upper regions of the atmosphere, and this, mingling with the warmer and moister air of the sea, forms very dense clouds. "In the northern hemisphere within the tropic, the barometer usually falls with a northerly wind, because whirlwinds come from the eastward. But in the southern hemisphere within the tropic, the barometer usually falls with a southerly wind, because, although whirlwinds there also come from the eastward, they revolve in a contrary direction, south of the equator. In both hemispheres, revolving gales blow with a west wind on the side next the equator. In recurving in both hemispheres, whirlwind storms will have a polar direction for a while. The barometer, during that time, will begin to fall with easterly winds; but after they have recurved, and are moving easterly, the barometer will fall with southerly winds in the northern hemisphere, and with northerly winds in the southern hemisphere." There may, however, be exceptions to these general rules. "Ships at sea may sail into whirlwind gales at any point in their circumference; and they not unfrequently overtake storms in their course by sailing faster than these move along." Moreover, these storms have not always an easterly progression in high latitudes, and they become more or less irregular on coming in contact with hills and valleys on land, as already noticed.

To show the value of attending to the indications of the barometer at sea, we will state briefly the facts of a case in which Capt. J. V. Hall avoided falling into the heart of one of these gales or typhoons of the China Sea. When three or four days' sail from Macao, about noon, Captain Hall observed "a most wild and uncom

mon-looking halo round the sun." Next day set in with light squalls, smooth water, but strong ripples. The afternoon was remarkably fine, but the barometer had fallen considerably since noon. About 3 P.m. it

was still falling; and although the weather was very fine, orders were given to strike the sails, and to clear the rigging of everything that could be spared: the boats were also hoisted on board, and well secured. Towards evening, a bank was observed in the S.E. Night closed in, and the water continued smooth; but the sky looked wildish, the scud coming from the N.E., the wind from North. "I was much interested in watching for the commencement of the gale, which I now felt sure was coming; and considering the theory to be correct, it would point out my position with respect to its centre. That bank in the S.E. must have been the meteor [storm] approaching us, the N.E. scud the outer north-west portion of it; and when at night a strong gale came on about N. or N.N.W., I felt certain we were on its western and southern verge. It rapidly increased in violence; but I was pleased to see the wind veering to the N.W., as it convinced me that I had put the ship on the right tack, namely, on the starboard tack, standing, of course, to the S.W. From 10 A.m. to 3 P.m. it blew with great violence; but the ship, being well prepared, rode comparatively easy. The barometer was now very low, the wind about W.N.W., the centre of the storm passing, doubtless, to the northward of us, and to which we might have been very near, had we in the first part put the ship on the port tack, and stood to the northeast and towards the centre, instead of on the starboard tack, and to the south-west, the opposite direction. About 5 P.m. wind at W.S.W., sensibly decreasing, the barometer rising. At 6, fresh gale; made sail to keep

ship steady: a very great sea on, and towards midnight it became a moderate gale. The wind having now become S.W. to S.S/W., the ship broke off to S.E. Thinking it a pity to be lying so far out of our course, I wore to N.W., and made sail; but in less than two hours heavy gusts came on, and our barometer began again to fall. I now thought, of course, we were approaching the storm again. I wore again to the S.E.; and to show more clearly how great a difference a very short distance nearer to or farther from these storms makes, the weather rapidly improved. The next morning it was fine and moderate, and the wind became S.E. with a heavy running westerly swell. Until the afternoon, there was a dark, wild appearance to the westward, which seemed to me another proof that it was the meteor which had the day before appeared in the S.E., and whose course had been from S.E. to N.W., passing a little northward of our position."

There are many other interesting points which might be noticed, did the narrow limits of this Essay permit. We may, however, quote the following. simple practical result of observation, namely, "that when ships meet a whirlwind gale, and are sailing towards its centre, north of the equator, they always have the wind on the ship's port-side; and when ships meet a whirlwind gale south of the equator, and are sailing towards its centre, they always have the wind on the ship's starboard-side." "But when the first part of a revolving gale is overtaking a ship, it will be otherwise; for then the ship would be as if sailing from the storm's centre. This would be the relation of the ship to the wind, until the storm's centre had passed beyond the ship's place, after which the ship would be as if pursuing the gale."

RECENT RESEARCHES IN THE LAW OF STORMS AND
SUMMARY OF RULES.

Franklin had perceived that the views prevalent in his day respecting the nature of storms and hurricanes could not be correct; but he did not make much progress towards developing anything better. Subsequently Capper, from observations in the East, published many sound and suggestive notions on the subject; but Redfield, Reid, Thom, and Piddington were really the first investigators and luminous expositors of what has since come to be known as the Law of Storms. They took ships' logs and barometers into their confidence—both very imperfect and inaccurate data in those days on which to found a theory—and they eventually succeeded in discovering that every hurricane and great storm had a central spot of very low pressure, where there was a calm, and around which the winds were blowing with varying but intense strength; that the general direction of the wind was against the motion of watch hands in the northern hemisphere, but with watch hands in the southern hemisphere; that there was also a progression of the storm area; and that the pressure increased towards the outer verge of the storm. These things being determined, they gave their attention to showing how ships might best avoid the worst and most destructive parts of the hurricane.

But it must not be supposed that they were devotees of the circular theory of the wind blowing in circles returning on themselves—and of the centre being eight voints from the direction of the wind, such as has been the teaching of the last thirty years: all this they repudiated, and Colonel Reid distinctly states that if a circle represented a whirlwind correctly when station

ary, "in the progressive whirlwind the figure would become cycloidal, and the degree of curvature would depend upon the rate of progress of the storm;" he also remarks that "in attempting to lay down a storm's track, a wrong judgment may be formed if data be rejected on account of its not conforming to a figure exactly circular;" but that circles were found to be the most convenient figures in endeavouring to explain the nature of storms: nothing more—and Redfield, Thom, and Piddington were equally opposed to the strictly circular theory.

When our elder cyclonists propounded the law of storms they had little idea that they had in reality discovered the law of the winds everywhere and always; that no strong wind blows in any part of the world but what is of the type of the cyclone; that the wind in the tropical hurricane may at times develop greater force and velocity than extra-tropical storms, but that they are all of one character—both as regards the rotation of the wind, and the progression (bodily) of the area of low pressure; thus they paved the way for the advanced theories of Dove, and for the later exposition of the law of the wind in relation to the distri-. bution of atmospheric pressure as enunciated by Galton and Buys Ballot.

Spiral Rotation of the Wind.—As the result of careful research, modern meteorologists, almost without exception, recognise the spirally incurving tendency of the wind as its most probable behaviour in a storm; the circulation being around and at the same time more or less towards the centre of least pressure, which is usually characterised by a calm. The direction in which the winds move round this centre is—in the northern hemisphere from right to left (against the sun), or contrary to the motion of the hands of a watch,—but