Part 3

OUR old English Almanacks have a Maxim to this Purpose.

If woolly Fleeces spread the Heavenly Way, Be sure no Rain disturbs the Summer Day.

AND Pliny to the same Purpose.[c]

SI Sol oriens cingetur Orbe, & postea totus defluxerit aequaliter, Serenitatem dabit.

That is,

IF the rising Sun be incompassed with an Iris, or Circle of white Clouds, and they equally fly away, this is a Sign of fair Weather.

THERE is another English Proverb worth remembering.

In the Decay of the Moon, A cloudy Morning bodes a fair Afternoon.

IV.

Large like Rocks.----Great Showers.

IN the old Almanacks we have this Sign of the Weather thus expressed.

When Clouds appear like Rocks and Towers, The Earth's refresh'd by frequent Showers.

THE Reason of this seems to be, that the watery Vapours are then condensed, or condensing, which gives them this rough and ragged Appearance, and as soon as the thin Films that retain the Water are broke by this Pressure, these heavy Clouds descend in Rain.

THESE Observations, as well as some that follow, are agreeable to all Climates, which is the Reason that they appear in so many different Authors, and have been taken notice of in so many Ages. This however does not at all diminish the Credit, or the Merit of our Shepherd's Observations, who certainly drew them not from Books, but from his own Experience, and therefore their agreeing so well with the Rules of other great Masters, ought to establish his Authority in such Cases as are not supported by alike concurrence from ancient or modern Writers, the Testimony of Nature is always sufficient Evidence.

If small Clouds increase----Much Rain.

THIS and the following Observation cannot well be understood, without giving some Account of Clouds in general. The Atmosphere is supposed to extend itself about five Miles round this Globe of Earth, and within that Space move all kind of Vapours exhaled by the Sun's Force, or protruded by the subterraneous Heat. The ascending of these Vapours into the Air, depends upon many things, and therefore as different as its Causes; for instance, their ascent depends in the first place on the degree of Heat with which they are drawn up or forced out; next upon the Lightness of the Vapours themselves; thirdly, on the Density or Rarity of the Air through which they pass; and lastly, on the Force and Direction of the Winds, which they encounter in their Passage.

ACCORDING to the Nature of these Vapours, and the Circumstance attending their Passage, they appear to us differently below. For if they be extremely subtile they mount very high, and there, according to the Sentiment of Sir Isaac Newton, form by Refraction the Azure, or blue Colour, that over-spreads the Sky in serene Weather. Clouds, while they remain visible, do not rise above the Height of a Mile; and we always observe, that the highest are of a very light Colour, and hardly seen. If, therefore, small Clouds increase, it shews, that the Disposition of the Air is such, as that these Clouds cannot rise therein, either from their own Weight, the want of a protrusive Force, or from the falling of the Wind, which in cloudy Weather is always a Sign of Rain.

VI.

If large Clouds decrease----Fair Weather.

THE same kind of Reasoning accounts very clearly for this Prognostick, since it shews, that the Vapours are either exhaled by the Sun's Heat, or are driven off by Winds, and so resolved into smaller Clouds, capable of ascending higher in the Atmosphere; all which are Circumstances that secure us from Rain, and afford us a certainty of fair Weather.

IT is, however, to be observed, that large black Clouds are frequently, in a Summer Evening, melted into Dews; and this much more frequently happens in the Autumn, because the Evenings are then cooler, and the Vapours more easily condensed for that Reason. In all Observations of this Sort, there is a great degree of Prudence and good Sense required to apply them, and hence it very frequently happens that such Observations are condemned as treacherous and abusive, merely because those who would employ them want the Sagacity which is requisite to understand them clearly.

VII.

MISTS. If they rise in low Ground and soon vanish. } Fair Weather.

THIS is a sure Sign and very well expressed, that is, clearly, and, in few Words, which is the Excellency of such Aphorisms. In order to be convinced of its good Sense and Certainty, we must consider a little what Mists are, whence they rise, and what becomes of them.

MISTS are, strictly speaking, uncompacted Exhalations, which while they fleet near the Earth are styled Mists, but when they ascend into the Air, are called Clouds. If therefore, rising out of low Ground, they are driven along the Plain, and are soon lost to the Sight, it must arise from some of these Causes. That there is an Air abroad sufficient to divide and resolve them, or the Heat of the Sun has been strong enough to exhale them, that is, to rarify them, so as to render them lighter than the Air through which they were to pass. Whichever way this happens the Maxim remains unimpeached.

VIII.

If they rise to the Hill-tops. } Rain in a Day or two.

WHEN Mists are very, heavy in themselves, and rise only by the Action of that protrusive Force, exerted by the subterranean Fire, they can rise no higher than where the Gravitation becomes superior to that protrusive force, for then they descend again by their own Weight, and this occasions the Appearance mentioned in the Observation of their hanging upon Hill-tops, where they are very soon condensed, and fall down in Rain.