« AnteriorContinuar »
the coast under consideration ; but it occurs with peculiar force on what is called the windward coast, especially at Sierra Leone. Its denomination is derived from the Portugese, it being a corruption of the word trueno, which means thunder-storm. Its approach is first discernible by the appearance of a small clear silvery speck, at a high altitude in the heavenly expanse, which increases and descends towards the horizon, with a gradual and slow, but visible motion. In its descent it becomes circumscribed by a dark ring, which extends itself on every side, and as soon as the silvery cloud approaches the horizon, veils it in impenetrable gloom. At the moment the elements seem to have ceased their operations, and the very functions of nature to be paralysed ; the atmosphere appears to be deprived of the spirit of vitality, and a sensation of approaching suffocation pervades and oppresses the physical system. The mind is wrapped in awe and suspense, but the latter is speedily relieved by the dark horizon being suddenly illuminated by one broad blaze of electric fluid ; peals of distant thunder then break upon the ear, and rapidly approach, and increase in fervency and violence, till the shocks become appaling ; when the thunder is at its loudest, a tremendous gust of wind rushes with incredible and often irresistible vehemence from the darkened part of the horizon, not rarely in its course carrying away roofs of houses and chimney-tops, blowing down or uprooting trees, and laying the stoutest and largest ships on their beam-ends, or sinking them under weigh or at anchor; and to that succeeds a furious deluge of rain, which falls in one vast sheet, rather than in drops, and concludes this terrible convulsion. The lightning is of the most vivid description, and, contrary to what has been reported of it, seldom sheet-lightning, but forked and piercing, and often extremely destructive, both to things animate and inanimate. Its apparently doubtful, wild course, is sometimes directed to a large and lofty tree, and the foliage, at the points of contact, is blasted on the instant, the exposed branches are severed from the trunk, and probably the enormous trunk itself is rent to its basis and destroyed. When it comes in contact with a house, it frequently leaves it as great a wreck as ships have been seen to be on coming out of a severe action, or after a destructive storm; and, occasionally, the building entered by it may happen to remain untouched, and its inmates, some, or all of them, as the author has known to occur, perish under its scorching influence. Occasionally the spindle of a ship's mast, the most elevated part of it, may appear to be the point of attraction, and it will sometimes dart among the spars and cordage harmless, descending till it reach the deck, when it suddenly quits the vessel by some aperture, and rapidly returning through another, seems to have acquired a new character with incredible velocity ; for, steering its strange and rapid course into the maindeck or hold, it will kill, maim, or injure every animate or inanimate with which it comes in contact. Much good has unquestionably been effected by conductors; but those who have watched the progress of the electric fluid, will hold the theorist in no estimation, who does not make the atmosphere the first and most important point of consideration. The heavy peals, or rather the terrifying shocks, of thunder which follow the lightning, frequently not only shake the buildings at Freetown, but the very foundations on which they stand; and the reverberations from the surrounding mountains increase, if possible, the awe excited by elementary commotion. The succeeding rain, or rather deluge, is happily of short duration, and rushing down the various inlets and indentations in the adjoining mountains, it forms into streams
a few minutes after its commencement, which sweeps through the streets of Freetown with astonishing velocity, bearing with them all the exposed vegetable and other matter, in a state of putridity or decay. Such is the tornado, and it is by the preponderating power of its gusts, and the atmospheric influence of lightning and its rains, that noxious exhalations from the earth, and deleterious miasmata, before confined to the neighbourhood of their origin by opposed or light currents of air in the day, or attracted by the land (the more lofty the more attractive) in the night, are removed, and consequently, the indescribably distressing feelings occasioned by a foul atmosphere, are superseded by those comparatively pleasurable and enlivening sensations which have been already noticed, pp. 40–42. The average time for the tornados to set in, is the termination of the month of September, from which time until Christmas, tolerably calm weather may be expected At Christmas, the periodical winds called the harmatan commence, and continue to blow for six or ten weeks. It is very curious, that whilst, to the natives, and to the Europeans, who, from long re-, sidence, may be said to be acclimated in the settlement, these winds are exceedingly annoying, the Europeans newly arrived consider them as refreshing and salubrious. But during the raging of the harmatans, the furniture of every house is covered with fine sand, and tables and chairs crack under their influence. Mr Boyle concludes this part of his subject by a diary of the weather at Sierra Leone, for the term nearly of a year,-a document that will be read with extreme interest by all the cultivators of meteorological science.
3. On the distance to which Spray of the Sea may be carried. -A few remarks on the distance to which spray from the sea is sometimes carried inland by storms of wind, may not, perhaps, be deemed altogether irrelevant to the subject we are treating upon. Sea-water is brought into the immediate neighbourhood of Manchester, which is at least thirty miles from the nearest coast, by every violent and long continued gale from the west ; and the exact proportion in given quantities of rain-water, collected on several occasions of this kind, has been determined chemically. That the sea is the principal source whence the salt is derived, with which the rain that falls in this town and its vicinity is occasionally impregnated, cannot, I think, be doubted; as I have clearly ascertained, by direct experiment, that its excess or deficiency depends entirely on the direction, force, and duration of the wind. Rain collected in clean glassvessels, a few miles to the north of Manchester, when the wind blows moderately from the north or north-east, scarcely ever exhibits the slightest trace of muriatic acid, on the application of the most delicate test (nitrate of silver), even when reduced two-thirds or three-fourths by spontaneous evaporation ; though samples collected in the town, precisely at the same time, on being subjected to the test, generally have their transparency more or less impaired. This fact seems to prove, that, notwithstanding muriate of soda is never raised into the atmosphere by evaporation, yet the air over large towns usually contains a very minute portion of muriatic acid, which, as Mr Dalton observes, is probably supplied by the sublimation of muriate of ammonia during the combustion of fuel. A considerable increase of mu
riatic acid takes place in the rain which falls in Manchester, when accompanied with a brisk breeze from the west, of several hours’ duration ; as is evident from the greater degree of opacity observed in samples caught under such circumstances, when treated with a few drops of the solution of nitrate of silver; and that which falls in the adjacent country, then manifests a sensible trace also. Indeed, the direction of the wind remaining the same, its force and duration seemn almost entirely to regulate the quantity of muriatic acid in the atmosphere; which completely establishes the fact that it is brought from the sea by the mechanical action of powerful currents of air. The utmost distance to which sea-water is conveyed by tempestuous winds is not easily determined. Sir H. Davy, in his Elements of Agricultural Chemistry, p. 295, states, that “ in great storms the spray of the sea has been carried more than fifty miles from the shore;” but he does not give his authority. Being at Blackwall, in Derbyshire, the residence of my relative John Blackwall, Esq. on the 23d of November 1814, when a violent hurricane occurred, which did extensive damage on the southern coast, I took several opportunities of examining the rain which fell at intervals on that occasion, and uniformly found that it became extremely turbid on application of the test, evidently containing much more muriatic acid than rain collected in large towns, during calm weather, is ever found to contain. The storm commenced on the night of the 22d of November, and continued, with little abatement, till after noon on the 23d. The wind blew from the south all the time, and the place of observation is 140 or 150 miles from the sea in that direction. This is, perhaps, the greatest distance on record to which sea-water has been clearly ascertained to be conveyed by the wind; and that it extended much further is highly probable. - Manchester Memoirs, vol. v. New Series.
4. Wild Animals in the Illinois Country, in North America. - The buffalo has entirely left us. Before the country was settled, immense prairies afforded pasturage to large herds of this animal, and the traces of them are still remaining in the o buffalo paths,” which are to be seen in several parts of the
State. These are well beaten tracts, leading generally from the prairies in the interior of the state, to the margins of the large rivers; shewing the course of their migrations as they changed their pastures periodically, from the low marshy alluvium to the dry upland plains. In the heat of sụmmer they would be driven from the latter by the prairie flies; in the autumn they would be expelled from the former by the mosquitoes; in the spring the grass of the plains would afford abundant pasturage, while the herds could enjoy the warmth of the sun, and snuff the breeze that sweeps so freely over them; in the winter, the rich cane on the river banks, which is an evergreen, would fur. nish food,—while the low grounds, thickly covered with brush and forest, would afford protection from the bleak winds. I know few subjects more interesting than the migration of wild animals, connecting, as it does, the singular display of brute instinct, with a wonderful exhibition of the various supplies which nature has provided for the support of animal life, under an endless variety of circumstances. These paths are narrow, and remarkably direct, shewing that the animals travelled in single file through the woods, and pursued the most direct course to their places of destination. -Deer are more abun. dant than at the first settlement of the country. They increase to a certain extent, with the population. The reason of this appears to be, that they find protection in the neighbourhood of man, from the beasts of prey that assail them in the wilderness, and from whose attacks, their young particularly can with difficulty escape. They suffer most from the wolves, who hunt in packs like hounds, and who seldom give up the chase until a deer is taken. We have often sat, on a moonlight summer night, at the door of a log-cabin on one of our prairies, and heard the wolves in full chace of a deer, yelling very nearly in the same manner as a pack of hounds. Sometimes the
would be heard at a great distance over the plain; then it would die away, and again be distinguished at a nearer point, and in another direction ;--now the full cry would burst upon us from a neighbouring thicket, and we would almost hear the sobs of the exhausted deer ;-and again it would be born away, and lost in the distance. We have passed nearly whole nights in listening to buch sounds; and once we saw a deer dash through the yard,