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.
THERE was formerly a very idle and ill grounded Distinction between moist and dry Exhalations, whereas in Truth all Exhalations are moist, or in other Words are watery Steams thrown off by Bodies respectively dry, and the former Distinction was invented only to solve these Phænomena of which we have been speaking, that is, the Mist rising and, dispersing without Rain, and the Mist condensed and resolved into Rain, which as I have shewn may be much better explained without any such Distinction.
IX.
A general Mist before the Sun rises, near the full Moon. } Fair Weather.
THIS is a general and a very extensive Observation, which enables us to judge of the Weather for about a Fortnight, and there is very great Reason to believe that it will very rarely deceive us. In order to convince the Reader of this, it will be necessary to explain, as far as we are able, the Causes of this.
MISTS are observed to happen when the Mercury in a Barometer is either very low of very high. They happen when it is high after the Region of the Air has continued calm a good while, and in the mean time a great Abundance of Vapours and Exhalations have been accumulated, making the Air dark by their quantity, and the disorderly Disposition of their parts. They happen when the Mercury is low, sometimes because the Rarity of the Air renders it unable to sustain the Vapours, which therefore descend and fall through it.