From this table it is seen that during the hurricane, which in all probability began a little to the north of Barbadoes on the evening of the 26th or morning of the 27th September, atmospheric pressure was above the average to the S.E. and E. of the region traversed by the storm. This being the case, the air would naturally flow from the high towards the low barometer that is, a general movement of the atmosphere would set in to the N.W., which was the course pursued by the storm for the first four days, a course at right angles to the usual trade-winds. During this part of its course, the rate at which it travelled was slow, not exceeding fifteen miles an hour. A progressive motion, as slow, nay often much slower, is common to these storms until they enter the region of the return trades, when the course is changed to N.E., the onward movement becomes greatly accelerated, and the storm itself spreads over a wider area.

571. Newspaper accounts of the weather before the hurricane describe it as close and sultry, the whole atmosphere being abnormally heated and excessively loaded with moisture. At Bermuda, at 9 A.M. of the 4th October, the temperature of the air was 79°.4, and the dew-point 73°.6, giving a humidity of 83: and this kind of weather had been prevailing for fully a week before. On the following day, the 5th, at 9 A.M., when the storm had just passed, the temperature was only 71°, the dew-point 56°, and the humidity 59°. Next night the temperature fell to 56°, whereas, before the storm, it did not fall on any night lower than 72°. It would be interesting to know if West Indian hurricanes occur simultaneously with a high pressure to the south, being thus interposed between that region and the usual position of the belt of calms at that season. If so, a considerable step will be gained toward understanding the causes of their origin, and how it is that they are, happily, phenomena of very rare occurrence.

572. Perhaps no writer on meteorology denies the influence of low pressures in drawing the wind towards them; but the effect of this influence in accounting for the rotation of storms

round their centres is often tacitly subordinated to a theory by which the storm is conceived to rotate from some force, not explained, but quite distinct from that arising from differences of pressure; and in virtue of which the air is driven to the outside of the whirl, thus diminishing the pressure at the centre, -much in the same way as, in whirling round a pail of water, part of the water leaves the centre and rises up against the sides of the vessel. In applying this theory to cyclones, the wind at every point within the storm is stated to be under the influence of two forces, the one arising from the rotatory motion of the cyclone, and the other from its progressive motion. To illustrate this by an example: Suppose a storm advancing over England to the eastward at the rate of twenty-five miles an hour, and taking the simplest case of the wind whirling round within the storm at the rate also of twentyfive miles an hour, then both the rotatory motion of the winds and the progressive motion of the storm are from the west, at the extreme south point of the storm; hence there the wind ought to be due west. At the extreme east point of the storm, since the direction of the wind due to the rotatory motion would be south, and by the progressive motion west, the wind ought to be seen blowing there from the south-west. At the extreme north, since the rotatory motion would be east, and the progressive west, and both being equal, there should be no wind at all. Lastly, at the extreme west point of the storm, the rotatory motion being north, and the progressive west, the wind should be northwest. Further, since in the south half of the storm the direction of the two motions is generally the same, and in the north half generally opposite, the gale ought to be most severely felt in the southern half of the cyclone, attaining its height at places immediately south, and least at those immediately north of the centre. When the rotatory motion much exceeds the progressive, the deviations from the true circular course of the winds when laid down on a synchronous chart would be less than those stated above; but in all cases, unless when the cyclone was stationary, the winds in the

front parts of the storm ought to be observed blowing out of the circular area of the storm. I am altogether at a loss to discover a storm to which this theory applies. If we look at the West Indian cyclone of October 1866, Plate VIII., we do not see any of the winds observed at 8 P.M. show even a tendency to blow in a direction in accordance with this theory, but, on the contrary, they all blow round and in upon the centre. To the European storm of the 2d November 1863, Plate VII., the same remark applies, as well as to every storm in tropical and temperate regions which I have examined by synchronous charts. The light winds which often prevail in the north-eastern part of European storms are sometimes referred to in illustration of this theory. In such cases it will be found, on examination, that there the isobarometric lines are considerably apart; but when it happens that the isobarometric lines are much crowded together on this side of the storm, the winds are strong and violent. The part of a storm where probably the winds are not so exactly proportioned to the difference of pressure, is that part of the front of the storm where the ascending current is strongest, thus diminishing the force of the surface-current; and that part in the rear where the air at the surface of the earth is coldest and driest, and where consequently the speed of the surface-current is increased.

573. It should be kept in mind that this theory was not arrived at through the slow and tedious process of a rigid induction-viz., by collecting the observations of the barometer and winds on synchronous charts, from which, their mutual relations having been observed, a theory was then constructed in strict accordance with the facts; but from observations, necessarily at the time few and scattered, it was inferred that the rotation of storms is circular. This inference necessitated another-viz., that the rotation is caused by some force or forces acting on the storm from without. Hence the theory proposed by the illustrious Dové, that storms are produced by the mutual lateral interference of two currents of air flowing in opposite directions. It is very difficult to imagine

how the polar and equatorial currents could be brought so to affect each other as they flow in opposite directions, that between them an atmospheric eddy or whirl 1200 miles in diameter could be formed rotating round its axis at the rate of 50 or 70 miles an hour. That storms often occur between these two great currents is undoubted; for in such cases the dry, heavy, polar current, by flowing under the moist, warm equatorial current, and thus thrusting it into the higher regions of the air, produces that disturbance in the atmospheric equilibrium which constitutes a storm. But what is maintained by the theory is this: By the lateral interference of these two currents, combined with the change in their direction produced by the rotation of the earth, a storm is formed.

574. In support of this theory, the great storm which occurred in the beginning of January 1855 is adduced. I have examined Dové's account of that storm,* and, from the Russian observations, Dr Buys Ballot's Jaarboek,' and other sources, have prepared eight synchronous charts of the weather of Europe from the 27th December 1854 to the 3d January 1855. From these charts the following facts regarding this singular storm appear: 1. It was for some time preceded by southerly winds, high temperatures, and low pressures over the north and north-west of Europe. 2. It originated in some locality within the arctic regions unknown. 3. It thence advanced over the Lofoden Islands, Stockholm, and Königsberg, to the Sea of Azov, its direction being thus from N.W. to S.E. 4. A high barometer prevailed to the west and south-west of its course, and another region of high barometer in eastern Russia and Siberia; these approached each other till the 29th December, after which they both fell back or gave way to the storm as it passed between them to the S.E. 5. The storm reached its greatest development on New Year's Day at noon, after which, as it proceeded on its course, its area became more contracted, and the depression at the centre became less. 6. In North Germany and Denmark, to the right hand of the storm's track, the

* See 'Law of Storms,' p. 258 et seq. London, 1862.

wind veered from S.W., by W. and N.W., to N.; and at Riga, St Petersburg, and other places to the east or left-hand side, it veered from S.E., by E. and N.E., to N.-these directions being in accordance with the law of the veering of the wind in the storms of the northern hemisphere. 7. In every one of the charts the wind is represented as blowing from the high to the low barometer, and modified by the change produced by the rotation of the earth; no other movement of the wind is observable than the spirally in-moving currents of air towards the area of least pressure. 8. On the 1st January, the pressure at Christiania being 28.410 inches, and at Greenwich, only 700 miles distant, 30.002 inches, a furious nor'-wester of unexampled violence descended over the North Sea on the north coasts of Germany and the Netherlands, and washed away part of Wangeroog, an island near the mouth of the Weser.

575. From a high barometer, on the 1st, in the west of Europe and in the east of the United States, and a low barometer and storm in California, Dové infers a barometric maximum extending over the whole Atlantic, and supposes that the storm in Europe on the one hand, and the storm in the west of America on the other, were produced by the lateral interference of equatorial currents with the polar current which was between them; and attention is drawn to the circumstance that the Californian storm came from the S.W. and the European from the N.W. It will be observed that the only observations from which a high barometer is assumed for the whole of the Atlantic are the barometers on its eastern and western shores. From Professor Alexis Caswell's observations at Providence, Rhode Island, America, it is seen that a heavy storm passed over that place to the east on the 29th December, when the barometer fell to 29.41, after which the wind veered from W. to N.W., the barometer rose, and the temperature fell. A storm from the west passed over Scotland on the 4th of January, and reached St Petersburg on the 6th. We need not here stop to inquire if these were one and the same storm, but only to remark that their occur