Chapter 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.

BUT none of these Cases agree with the Observation at the Head of the Page, and therefore to form a true judgment of the Weather, we must distinguish between them and the Case which explains the Observation.