Part 4

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 Phaenomena 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.

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.

If in the new Moon.----Rain in the old.

WHEN Exhalations rise copiously from the Earth into the Region of the Air, and the Air itself is in a proper Disposition, they ascend to a great Height, and continue a long Time before they are condensed, which accounts very clearly and philosophically for the Interval of fair Weather between the rising of these Mists, and their falling down again in Showers. Their ascending about Sun-rise is a Proof that the Air is thin, but at the same time of a Force sufficient to sustain them, since if the Mists were not specifically lighter than the Air itself they could not ascend.

WHEN the Moon is at the full, and such Exhalations rise plentifully, the time necessary for them to float in the Atmosphere, before they are condensed into Clouds and Rain, extends, generally speaking, beyond the Period of that Moon, and therefore the Observation directs us to expect fair Weather.

XI.

If in the old.----Rain in the New.

BUT as it is observed not only in this Climate, but all the World over, that great Changes of Weather happen near the Change of the Moon, it follows that this is the Season when these Exhalations that ascend so plentifully at Sun-rising are condensed, and consequently is the Season when we ought to expect Rain.

IF therefore the Exhalations rise in the new Moon, it is a Sign that the Air is in a fit disposition to sustain and support them for a considerable Time, and therefore we have Reason to expect that they should continue floating till the next regular change of Weather, that is, till the old of the Moon, or rather till towards the next Change, and therefore the Observation is very cautiously and very properly worded, directing us to expect Rain in the old, and in the new, and not at the old or new, because it is observed that these Changes of Weather happen not exactly at the Change of the Moon, but a Day or two before or after, of which the Reader will meet with many Examples in Captain Dampier's History of Winds and Storms at Sea.

XII.

WINDS. Observe, that in eight Years' Time there is as much South West Wind, as North East, and consequently as many wet Years as dry.

THIS must be allowed a very extraordinary Aphorism from a Country Shepherd, but at the same Time it is very agreeable to the Observations of Dr. Hooke, Dr. Derham, Dr. Grew, and other able Naturalists, who with unwearied Pains and Diligence have calculated the Quantity of Rain falling in one Year, and compared it with what fell in another. Lord Bacon, that Honour to our Nation and the Age which produced him, informs us, that it was an old Opinion there was a total Revolution of the Weather once in forty Years, and wishes it was inquired into. I cannot tell whether this has ever been done or not, but I think there is good Reason to conclude that there is a natural Balance established of wet and dry Weather, as of Light and Darkness, Heat and Cold, and other such like Variations.

IT may not be amiss to caution the Reader against a Mistake into which the Manner of this Rule being stated may easily lead him. It is this, that South West Winds cause Rain, and North East Winds fair Weather, which however is not a Thing clear or certain by any means. This indeed is true, that South West Winds and Rain, North East Winds and fair Weather come together, generally speaking. But the Question is, which causes the other, and a more difficult Question cannot easily be stated, because there seems to be Facts on both sides. South West Winds seldom continue long without Rain, this seems to prove the affirmative, but on the other Hand, when in hard Weather, Rain begins to fall, the Wind commonly veers to the South West, this looks as if the Rain caused the Wind.

BUT to keep close to the Shepherd's Observation. There is one Thing seems strongly to confirm it, which is this, that in any given Place the Quantity of Rain one Year with another is found to be the same by Experience, according to which the following Table has been calculated, for the mean Quantity of Rain falling one Year with another in those Places that are mentioned, and on this Proportion the other seems to be founded.

At Harlem 24 Inches Delf 27 Dort 40 Middleburg 33 Paris 20 Lyons 37 Rome 20 Padua 37-1/2 Pisa 34-1/4 Ulm 27 Berlin 19-1/2 In Lancashire 40 Essex 19-1/2

XIII.

When the Wind turns to North East, and it continues two Days without Rain, and does not turn South the third Day, nor Rain the third Day, it is likely to continue North East for eight or nine Days, all fair; and then to come to the South again.

IN my Opinion this and the subsequent Remarks depend entirely upon Observations, and may serve rather to found an Hypothesis, than seem be deduced from one. That the Variations of the Wind depend on certain Causes, and may consequently be reduced to Rules, is highly probable, and such Observations as these render it in a manner certain. But to explore these Causes, and to explain them in such a manner as to account for these Phaenomena in a satisfactory manner, requires not only great Sagacity but much Experience, and many Years' Observation, which, however, considering the great Benefits that would result to Mankind from establishing such a THEORY, would be Time well bestowed.

WE may however easily conceive that a constant North East Wind must be accompanied with fair Weather. For whatever the causes of Winds may be, yet on this side the Equator, a strong and settled North East always buoys up the Clouds and keeps them suspended. This has been long observed by, and passes for a settled point amongst Seamen. The Reason of it however cannot be so easily assigned, at least a satisfactory Reason, for as to Suppositions, every fanciful Man can furnish them at Pleasure.

THIS, as well as the following Observations, very plainly and clearly prove, that in this Part of the World fair Weather attends one Wind, and wet another, but which is the Cause and which the Effect, or whether both are not the Effects of some other Cause, I pretend not absolutely to determine. But inasmuch as it is certainly known, that Rains attend in other Climates those Winds that are here attended with fair Weather, it seems more agreeable to suppose that rainy Weather is occasioned chiefly by West Winds, because loaded with moist Vapours from the Sea.

XIV.

If it turn out again out of the South to the North East with Rain, and continues in the North East two Days without Rain, and neither turns South nor rains the third Day, it is like to continue North East for two or three months.

The Wind will finish these Turns in three Weeks.

THIS Observation is of the same nature with the former, and is plainly deduced from long experience. Our Author seems to contradict himself in saying that these Winds finish their Turns in three Weeks, but his true Meaning certainly is, that they are \about three Weeks in turning from the South to the North East again. Some very great men have laid it down as a thing certain, that the Variations of the Wind are to be accounted for by the Alteration of the Balance of the Air, occasioned by the different Effects of Heat and Cold; but other Writers again insist very copiously on the Effects which Winds have upon the Air, and thus confound us in a Circle of Causes and Effects, whence it is plain that they do not thoroughly understand the Subject themselves, and therefore it is no Wonder that they are not able to explain it to others.