South of the equator, hurricanes occur in November and May, and travel to the W.S.W., and afterwards, but not always, to the S. and S.E., the wind invariably moving round a central space (which is usually characterized by a calm) from left to right, or with the hands of a watch ; while the storm, has a diameter of 1 to 1500 miles, moves onwards at the rate of 1 to 20 miles, but more frequently 4 to 7 miles an hour, for a period a few hours to ten days, attended with torrents of rain, and its northern half often with lightning. Dr. Thom showed that south of the equator these rotatory storms are always generated between the N.1V. monsoon and S.E. trade-wind. They occur only during the: S.W. monsoon months, and their rise and progress are intimately connected with the S.E. trade-wind and N.W. monsoon, two opposing winds. With ships, the safest course is to lie to and watch the barometer and wind, till the bearing of the centre be known with some certainty.
Of those who have resided at Mauritius, who have earnestly studied and discussed the laws which govern these storms, may be mentioned Dr. Thom, Lieutenant Fryers, Royal Engineers, Mr. Sedgewick, who published a little work, which he called The True Principle, and Mr. Bosquett, of the Observatory at Mauritius, who translated into French Piddington's Hornbook, with annotations of his own, and who claimed to be able, by care ful and constant. meteorological observations, to foretell the occurrence of hurricanes in the Indian Ocean, and to describe the course they will take, The chart in Piddington's Hornbook, shows that, these cyclones never extend to the northward of or south latitude in the meridian of Maur itius. Therefore vessels leaving the island in the.
hurricane season for any part of India, should steer to the northward, passing well to the west ward of the Cargades, a most dangerous group, thus keeping a clear sea open to the westward, that there may be nothing ht the way should it be desirable to run to the northward and west ward, which would be the true course to take in case of encountering the south-western or north western quadrants of a cyclone (of which in the hurricane season a vessel from Mauritius is in danger), and this course she should keep until she is sufficiently far north to be beyond its influence, Of the more remarkable occurrences, that at the mouth of the Ganges, on the 7th October 1737, was attended by a violent earthquake, and extended GO miles up the river ; 20,000 craft of all descrip tions were destroyed,—amongst them, 8 English ships and all their crews,—and 300,000 souls are said to have perished in Lower Bengal, or in the bay. The river rose 40 feet above its usual
level. An English church and steeple sank into the earth the next morning.
On 4th October 1739, a cyclone occurred at Ganges mouth, in which 80,000 lives were lost.
Madras has been subjected to severe hurricanes, generally in the early part of May or the end of October. They seem to travel up from the E.S.E., and progress rapidly in a W.N.1V. direction till they touch the land, and then they assume a westerly or sometimes W.S.1V. course. Their centres generally come right on to the port of Madras. A hurricane has seldom been known to extend south of Porto Novo, 120 miles from Madras (out at sea they are met with as far south as Ceylon), or north of Nellore, 100 miles from Madras. Their diameters are about 150 miles, and they revolve in a direction contrary to the hands of a watch. When the hurricane's centre comes right on to Madras, and there takes a west course, the wind is first at N., increasing in violence for a few hours, and then a lull or perfect calm for half an hour or so, when the hurricane recom mences furiously from the exactly opposite quarter, south. This is in accordance with the theory of cyclones. Usually the gale commences about N.N.W., showing that the vortex of the cyclone bears about E.N.E. Vessels, therefore, warned by the barometer, tho hollow breaking surf, the threatening sky, and the signals of the master attendant, should at once put to sea (having pre viously close-reefed and sent down top-hamper). The course to steer, and fortunately it is one which the wind assists, is S.S.E. to S.E. In a few hours the vessel will probably have the wind moderate at west, and may—in fact it has been done—sail round the cyclone, the wind veering to south and then to east. Vessels at first steer ing east to get away from the land have run right into the vortex of the hurricane. The only danger in a southerly course is from the storm wave setting the ship on shore. If the lead give notice of this, the ship must be hauled up more to the eastward.
If the gale commence N.N.W. at Madras, and end at S.E., as has often happened, it shows that the centre has taken a W.S.1V. course, and a little to the south of the town; but if it end at S.W., it shows that the centre has taken a course, and the vortex passed to the north of Madras.