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WATER-SPOUT (continued)
There appeared, not far from the mouth of the harbour of St. John's, two or three water-spouts, one of which took its course up the harbour. Its progressive motion was flow and unequal, not in a strait line, but as it were by jerks or starts. When just by the wharf, I stood about 100 yards from it. There appeared in the water a circle of about twenty yards diameter, which to me had a dreadful though pleasing appearance. The water in this circle was violently agitated, being whisked about, and carried up into the air with great rapidity and noise, and reflected a lustre, as if the sun shined bright on that spot, which was more conspicuous, as there appeared a dark circle around it. When it made the shore, it carried up with the same violence energies, slaves, large pieces of the roofs of houses, &c. and one small wooden house it lifted entirely from the foundation on which it stood, and carried it to the distance of fourteen feet, where it settled without breaking or oversetting; and, what is remarkable, though the whirlwind moved from west to east, the house moved from east to west. Two or three negroes and a white woman were killed by the fall of the timber, which it carried up into the air, and dropt again. After passing through the town, I believe it was soon dissipated; for, except tearing a large limb from a tree, and part of the cover of a sugar-work near the town, I do not remember any further damage done by it. I conclude, wishing you success in your enquiry, and am, &c."A fluid moving from all points horizontally towards a center must, at that center, either mount or descend. If a hole be opened in the middle of the bottom of a tub filled with water, the water will flow from all sides to the center, and there descend in a whirl. But air flowing on or near the surface of land or water, from all sides towards a center, must at that center ascend; because the land or water will hinder its descent.
If these concentring currents of air be in the upper region, they may indeed descend in the spout or whirlwind; but then, when the united current reached the earth or water, it would spread, and probably blow every way from the center. There may be whirlwinds of both kinds; but from the effects commonly observed, Dr. Franklin suspects the rising one to be most frequent: when the upper air descends, it is perhaps in a greater body extending wider, as in thunder-gusts, and without much whirling; and when air descends in a spout or whirlwind, he conceives that it would rather press the roof of a house inwards, or force in the tiles, shingles, or thatch, and force a boat down into the water, or a piece of timber into the earth, than snatch them upwards, and carry them away.
The whirlwinds and spouts are not always, though most frequently, in the day-time. The terrible whirlwind which damaged a great part of Rome, June 11 1749, happened in the night; and was supposed to have been previously a water-spout, it being asserted as an undoubted fact, that it gathered in the neighbouring sea, because it could be traced from Ostia to Rome.
This whirlwind is said to have appeared as a very black, long, and lofty cloud, discoverable, notwithstanding the darkness of the night, by its continually lightning, or emitting flashes on all sides, pushing along with a surprising swiftness, and within three or four feet of the ground. Its general effects on houses were, stripping off the roofs, blowing away chimnies, breaking doors and windows, forcing up the floors, and unpaving the rooms, (some of these effects seem to agree well with the supposed vacuum in the center of the whirlwind) and the very rafters of the houses were broke and dispersed, and even hurled against houses at a considerable distance, &c.
The Doctor, in proceeding to explain his conceptions, begs to be allowed two or three positions, as a foundation for his hypothefis. 1. That the lower region of air is often more heated, and so more rarified, than the upper; and by consequence specifically lighter. The coldness of the upper region is manifested by the hail, which sometimes falls from it in warm weather. 2. That heated air may be very moist, and yet the moisture so equally diffused and rarified as not to be visible till colder air mixes with it, at which time it condenses and becomes visible. Thus our breath, although invisible in summer, becomes visible in winter.
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© Derived from Thomas Cadell's new corrected edition, London: 1780, page 314, 2003
Prepared by Paul Turnbull
http://southseas.nla.gov.au/refs/falc/1479.html