Having already discussed, in the course of this work, the phenomena of the meteors above mentioned, we shall at present communicate a few simple rules, which may serve to prognosticate the weather, or to ascertain its future variations, with tolerable accuracy. For this purpose, Mr. Kirwan (" Transactions of the Royal Irish Academy, " vol. v.) has laid down the following plan, from observations that had been made in England, during a period of 112 years; namely, from 1677 to 1789.
l. When no storm has either preceded or followed the vernal equinox, the succeeding summer is in general dry, or at least so, five times out of six.
2. If a storm happen from an easterly point, on the 19th, 20th, or 21st day of May, the ensuing summer will, four times in five, be also dry. - The same event generally takes place, if a storm arise on the 25th, 26th, or 27th days of March, in any point of the compass.
3. Should there be a storm, either at south-west, or at west-south-west, on the 19th, 20th, 21st, or 22d of March, the following summer is wet, five times out of six.
In England, if the winters and springs be dry, they are mostly cold; but, if moist, they are generally warm : on the contrary, dry summers, and autumns, are usually hot; as moist summers are cold. Thus, if the humidity or dryness of a particular season be determined, a tolerably correct idea may be formed respecting its temperature. - To these indications may be added the following maxims ; which, being the result of observations made by accurate inquirers, may so far be depended upon, as they will afford a criterion of the mildness, or severity, and of the dryness or moisture, of future seasons.
I. A moist autumn, succeeded by a mild winter, is generally followed by a dry and cold spring; in consequence of which, vegetation is greatly retarded.
2. Should the summer be uncommonly wet, the succeeding winter will be severe ; because the heat or warmth of the earth will be carried off by such unusual evaporation. Farther, wet su mers are mostly attended with art increased quantity of fruit on the white-thorn, and dog-rose; nay, the uncommon fruitfulness of these shrubs is considered as the presage of an intensely cold winter.
3. A severe winter is always indicated by the appearance of cranes and other birds of passage, at an early period in autumn ; because they never migrate southwards, till the cold season has commenced in the northern regions.
4. If frequent showers fall in the month of September, it seldom rains in May; and the reverse.
5. On the other hand, when the wind often blows from the south-west, during either summer or autumn; when the air is unusually cold for those seasons, both to our sensations, and by the thermometer; at the same time, the mercury being low in the barometer; - under these conditions, a profuse fall of rain may be expected.
6. Great storms, rains, or other violent commotions of the clouds, produce a kind of crisis in the atmosphere ; so that they are attended with a regular succession, either of fine or of bad weather, for some months.
lastly, an unproductive year mostly succeeds a rainy winter; as a rough and cold autumn prognosticates a severe winter. - See also the article Climate.