WEATHER
, denotes the state or disposition of the atmosphere, with regard to heat and cold, drought and moisture, fair or foul, wind, rain, hail, srost, snow, fog, &c. See Atmosphere, Hail, Heat, Frost, Rain, &c.
There does not seem in all philosophy any thing of more immediate concernment to us, than the state of the Weather; as it is in, and by means of the atmosphere, that all plants are nourished, and all animals live and breathe; and as any alterations in the density, heat, purity, &c, of that, must necessarily be attended with proportionable ones in the state of these.
The great, but regular alterations, a little change of Weather makes in many parts of inanimate matter, every person knows, in the common instance of barometers, thermometers, hygrometers, &c; and it is owing partly to our inattention, and partly to our unequal and intemperate course of life, that we also, like many other animals, do not feel as great and as regular ones in the tubes, chords, and fibres of our own bodies.
To establish a proper theory of the Weather, it would be necessary to have registers carefully kept in divers parts of the globe, for a long series of years; from whence we might be enabled to determine the directions, breadth, and bounds of the winds, and of the weather they bring with them; with the correspondence between the Weather of divers places, and the difference between one sort and another at the same place. We might thus in time learn to foretell many great emergencies; as, extraordinary heats, rains, frosts, droughts, dearths, and even plagues, and other epidemical diseases, &c.
It is however but very few, and partial registers or accounts of the Weather, that have been kept. The Royal Society, the French Academy, and a few particular philosophers, have at times kept such registers as their fancies have dictated, but at no time a regular and correspondent series in many different places, at the same time, followed with particular comparisons and deductions from the whole, &c. The most of what has been done in this way, is as follows: The volumes of the Philosophical Transactions from year to year; the same, for instructions and examples pertaining to the subject, vol. 65, part 2, art. 16; Eras. Bartholin has observations of the Weather for every day in the year 1671: Mr. W. Merle made the like at Oxford, for 7 years: Dr. Plot did the same at the same place, for the year 1684: Mr. Hillier, at Cape Corse, for the years 1686 and 1687: Mr. Hunt and others at Gresham College, for the years 1695 and 1696: Dr. Derham at Upminster in Essex, for the years 1691, 1692, 1697, 1698, 1699, 1703, 1704, 1705: Mr. Townley, in Lancashire, in 1697, 1698: Mr. Cunningham, at Emin in China, for the years 1698, 1699, 1700, 1701: Mr. Locke, at Oats in Essex, 1692: Dr. Scheuchzer, at Zurich, 1708; and Dr. Tilly, at Pisa, the same year: Professor Toaldo, at Padua, for many years: Mr. T. Barker, at Lyndon, in Rutland, for many years in the Philos. Trans.: Mr. Dalton for Kendal, and Mr. Crosthwaite for Keswick, in the years | 1788, 1789, 1790, 1791, 1792, &c; and several others. The register now kept, for many years, in the Philos. Trans. contains an account, two times every day, of the thermometer, barometer, hygrometer, quantity of rain, direction and strength of the wind, and appearance of the atmosphere, as to fair, cloudy, foggy, rainy, &c. And if similar registers were kept in many other parts of the globe, and printed in such-like public Transactions, they might readily be consulted, and a proper use made of them, for establishing this science on the true basis of experiment.
From many experiments, some general observations have been made, as follow: That barometers generally rise and fall together, even at very distant places, and a consequent conformity and similarity of Weather; but this is the more uniformly so, as the places are nearer together, as might be expected. That the variations of the barometer are greater, as the places are nearer the pole; thus, for instance, the mercury at London has a greater range by 2 or 3 lines than at Paris; and at Paris, a greater than at Zurich; and at some places near the equator, there is scarce any variation at all. That the rain in Switzerland and Italy is much greater in quantity, for the whole year, than in Essex; and yet the rains are more frequent, or there are more rainy days, in Essex, than at either of those places. That cold contributes greatly to rain; and this apparently by condensing the suspended vapours, and so making them descend: thus, very cold months, or seasons, are commonly followed immediately by very rainy ones; and cold summers are always wet ones. That high ridges of mountains, as the Alps, and the snows with which they are covered, not only affect the neighbouring places by the colds, rains, vapours, &c, which they produce; but even distant countries, as England, often partake of their effects. See a collection of ingenious and meteorological observations and conjectures, by Dr. Franklin, in his Experiments, &c, pa. 182, &c. Also a Meteorological Register kept at Mansfield Woodhouse, from 1784 to 1794, Nottingham 1795, 8vo; and Kirwin's ingenious papers on this subject in the Transactions of the Irish Academy, vol. 5. See also the articles Evaporation, Rain, and Wind.
That a thick dark sky, lasting for some time, without either sun or rain, always becomes first fair, and then foul, i. e. it changes to a fair clear sky, before it turns to rain. And the reason is obvious: the atmosphere is replete with vapours which, though sufficient to reflect and intercept the sun's rays from us, yet want density to descend; and while the vapours continue in the same state, the Weather will do so too: accordingly, such Weather is commonly attended with moderate warmth, and with little or no wind to disturb the vapours, and a heavy atmosphere to sustain them; the barometer being commonly high: but when the cold approaches, and by condensing the vapours drives them into clouds or drops, then way is made for the sun beams; till the fame vapours, by farther condensation, be formed into rain, and fall down in drops.
That a change in the warmth of the Weather is followed by a change in the wind. Thus, the northerly and southerly winds, though commonly accounted the causes of cold and warm Weather, are really the effects of the cold or warmth of the atmosphere; of which Dr. Derham assures us he had so many confirmations, that he makes no doubt of it. Thus, it is common to see a warm southerly wind suddenly changed to the north, by the fall of snow or hail; or to see the wind, in a cold frosty morning, north, when the sun has well warmed the air, wheel towards the south; and again turn northerly or easterly in the cold evening.
That most vegetables expand their flowers and down in sunshiny Weather: and towards the evening, and against rain, close them again; especially at the beginning of their flowering, when their seeds are tender and sensible. This is visible enough in the down of Dandelion, and other downs: and eminently so in the flowers of pimpernel; the opening and shutting of which make what is called the countryman's Weatherwiser, by which he foretels the Weather of the following day. The rule is, when the flowers are close shut up, it betokens rain, and foul Weather; but when they are spread abroad, fair Weather.
The stalk of trefoil, lord Bacon observes, swells against rain, and grows more upright: and the like may be observed, though less sensibly, in the stalks of most other plants. He adds, that in the stubble fields there is found a small red flower, called by the country people pimpernel, which opening in a morning, is a sure indication of a fine day.
It is very conceivable that vegetables should be affected by the same causes as the Weather, as they may be considered as so many hygrometers and thermometers, consisting of an infinite number of tracheæ, or air-vessels; by which they have an immediate communication with the air, and partake of its moisture, heat, &c.
Hence it is, that all wood, even the hardest and most solid, swells in moist Weather; the vapours easily insinuating into the pores, especially of the lighter and drier kinds. And hence is derived a very extraordinary use of wood, viz, for breaking rocks or milstones. The method at the quarries is this: Having cut a rock into the form of a cylinder, the workmen divide it into several thinner cylinders, of horizontal courses, by making holes at proper distances round the great one; into these holes they drive pieces of sallow wood, dried in an oven; these in moist Weather, imbibing the humidity from the air, swell, and acting like wedges they break or cleave the rock into several flat stones. And, in like manner, to separate large blocks of stone in the quarry, they wedge such pieces of wood into holes, forming the block into the intended shape, and then pour water upon the wedges, to produce the effect more immediately.
Weather-Glasses, are instruments contrived to shew the state of the atmosphere, as to heat, cold, moisture, weight, &c; and so to measure the changes that take place in those respects; by which means we are enabled to predict the alteration of Weather, as to rain, wind, frost, &c.
Under the class of Weather-glasses, are comprehended barometers, thermometers, hygrometers, manometers, and anemometers. |
