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I. The Storms of the Torrid Zone and their Extension into the Temperate Zones.

THE idea that any considerable diminution in the pressure of the atmosphere must be the result of some unusual disturbance in that medium, offers itself naturally to our mind, and it has, therefore, been long since maintained by those who observed that the weight of the atmosphere varied at different times. Otto von Guericke had attached a scale to the water barometer which he had invented in order to measure these variations, and quotes in chap. xxi. of the 'Mirabilia Magdeburgica,' in Schott's "Technica Curiosa,' a remarkable observation:-'In the year 1660 the air became so unusually light, that the finger of the little figure indicated a point below the lowest mark on the glass tube. When I saw this, I said to the persons who were present that, without doubt, a violent storm had arisen somewhere or other. Two hours had hardly passed when that storm burst over the country, although with less fury than it had exhibited on the ocean.' A more modern instance of the same fact is given by the storm of January 17, 1818, whose fearful ravages could be traced by me in the year 1827 in the forests of Prussian Lithuania, nearly ten years after the time when its devastations were felt from the coast of England to Memel, over an area of 1,100 miles in length and 190 in breadth. On January 18, the barometer at Königsberg fell 0·71 in. in eight hours, and between the

3rd and 17th 1·865 in. in all. In Dantzic it fell 1.598 in. In Edinburgh also, where the effects of the storm were such as are usually only produced by electrical explosions, the fall of the barometer was very great. In fact, the remark of Otto von Guericke has been so abundantly confirmed by the experience of the two centuries which have elapsed since his time, that the lettering attached to our barometers at the present day usually ends with the words 'stormy.'

The truth of these rules is not confined to the temperate zone. Scoresby earnestly recommends the use of the barometer to the seamen whom the whale fishery attracts to the dangerous waters of high latitudes. In consequence of a fall of his marine barometer of 0.825 in., on April 5, 1819, in lat. 70° 49′ N., long. 70° 15′ W., he was warned of and escaped a storm, which raged for two days incessantly. Similarly, several instances are given from the Trade-wind zone and the district of the Monsoons, in which an unusual diminution of pressure preceded West India hurricanes and typhoons. On July 26, 1825, the same fact was observed when Basseterre in Guadaloupe was destroyed by a storm, of whose violence some idea may be formed from the report of Gen. Baudrant, in which it is stated that three twentyfour pounders were blown away by it, and that a piece of deal board, 37 inches long, 9 inches wide, and 7 inch thick, was driven through a palm tree 16 inches in diameter.* Similar atmospherical conditions accom

It sometimes happens that whirlwinds of smaller dimensions produce extraordinary mechanical effects. Such a storm, whose diameter was only a quarter or half an English mile, passed, on April 8, 1833, between Calcutta and the great salt-water lake, about three miles to the eastward of the city. It was felt over an area sixteen miles in length, and in the course of four hours killed 215 persons, wounded 223, and blew down

panied a fall of the barometer of 1154 in. at St. Thomas, on September 29, 1819. On August 2, 1837, at 4 o'clock P. M., the harbour-master of Porto Rico notified to the masters of vessels that they ought to prepare for a storm, as the barometer was falling considerably. At 8 o'clock P. M. it had fallen to 29-601 in.; at 11 o'clock to 29-300; and ultimately to 28.0 in. The fall was about the same as at St. Thomas, where it fell from 29.930 to 28-064 in. during the same storm. All the precautions were in vain. Not a single one of the 33 ships which were lying at anchor could be saved, for the storm was of such violence that 250 houses were destroyed in St. Bartholomew alone. The ruin at St. Thomas was still more fearful, as the wrecks of 36 ships bestrewed the harbour, and the fort at its entrance was as much shattered as if it had been exposed to a bombardment. In this case, too, some twenty-four pounders were blown away. A large well-built house was torn from its foundations and left standing upright in the middle of the street, while other houses were completely blown down. We read in the Annales Maritimes' (ii. 550) the following account of the storm of January 26, 1825, at Guadaloupe:— Five ships, which had lain at anchor in the roads of Basseterre, disappeared, and only two of the captains were saved: one of them, Mackeown, saw his brig, after a struggle with the raging sea, carried up by a whirlwindfaire, pour ainsi dire, naufrage dans les airs (to be wrecked, so to speak, in the air).' The phenomena which accompany the storms of the Indian Ocean are precisely

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1,239 fishermen's huts. It forced a long bamboo cane through a wall five feet thick, so as to pierce the facing of the wall on both sides. The editor of the India Review remarks that a six-pounder could hardly have produced the same effect.

analogous to those just mentioned. In the night between February 28 and March 1, 1818, the barometer fell at the Mauritius, during the hurricane, to the level of 28.064 in. (reduced to the height at the sea-level).* It fell almost as low during the hurricane of March 1836. On the 6th, at 5 A. M., its height was 29.930 in., and by 8 o'clock on the morning of the 8th it had fallen to 28.229 in. Here, too, the force of the wind was almost incredible. The Theatre was a T-shaped building, and the body of the house, which was 82 feet in length and 34 in breadth, was torn from the façade on March 1, 1818, and removed to a distance of 5 feet from its foundations.

Whenever two occurrences constantly take place together, we may, with some probability, conjecture that they are mutually connected in the relation of cause and effect. We cannot decide which of them is the cause and which the effect, as it is not impossible that they may both be the results of some third primal cause. We are equally unable to decide immediately whether, even if one of the occurrences may have been directly the result of the other, the same effect might not have been brought about in a different manner.

Barometrical minima constantly occur when there is a considerable disturbance of the atmosphere. We see, however, that the level of that instrument is frequently very low at a time when mild spring winds seem to waft us from the severity of winter into a more genial season. Observers found it hard to convince themselves that so

*In the account we read, 'Jamais on ne l'avait vu aussi bas. Plusieurs personnes crurent que leurs baromètres étaient dérangés, celles qui ne pouvaient se méprendre sur la cause de cette dépression, s'attendaient à une grande catastrophe.' (It had never been seen so low before. Many persons thought that their barometers were out of order, while those who could not be mistaken as to the cause of the depression expected a great catastrophe.)