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the falling of a stick: but as the first side that meets the wind, throws the force of the wind upon the lower side; and this again throws it into the vacuities; this lower side receives the chief impulse of the wind; whence the rotation presently begins on that part: for it is not the first impulse of the wind in front;* but a lateral impulse, after the compression, that begins the

motion.

To this purpose we made several experiments upon paper-sails, turned with the blast of bellows. 1. And first, we added a fold to the lower side of the sail turning away from the blast, which now coming side-ways, might have a larger surface to strike against: but this had no good effect; the additional fold not assisting the percussion of the wind, so much as it hindered the sails from cutting the air. 2. Next we placed obstacles at some distance behind the sails, the whole breadth of them all; that the wind being more compressed, might strike the stronger : but this rather did harm: as the repercussion checked the primary motion. 3. Lastly, we made the sails double their former width, that the wind might be compressed the more; and have a stronger lateral percussion: and this succeed

** Which directly tends to overset the mill.

H

ed extremely; so that the sails turned with a much gentler blast; and revolved with a far greater velocity.

PRECEPTS.

Perhaps this increase of motion may be more commodiously procured by six or eight sails, than by four of twice the breadth; unless the bulk should be too great for the motion. But of this let trial be made.*

The length of the sails also contributes to the motion: for in all rotations, a small force applied towards the circumference, is equal to a much greater towards the centre. But the lengthening of the sails has this inconvenience, that the longer they are, the wider they stand from one another at top; and the less the wind is compressed. It might perhaps succeed to have the sail somewhat long, and widening towards the top, like an oar: but this we have not tried.

ADMONITIONS.

If these experiments be reduced to practice in wind-mills, the whole machine must have strength in its structure; especially in its foundation for the more the wind is compressed,

Enquire the success of a full circle of sails, placed valve-fashion, for the wind to slip through; as in the windmill at Deptford-bridge, near London.

though it whirls the sails round the faster; yet it also gives the greater shock to the mill.

It is reported, that there are, in certain parts, wind coaches, or caravans, driven with sails; which is an affair that should be well enquired into.*

PRECEPT.

Carriages to move by the wind 'are impracticable, except in plains, and open places. And even here also, what must be done when the wind fails? It is more rational to think of easing the motion of waggons, and carriages, by moveable sails, to take up and down; which might favour the horses, and ease their labour; than pretend to drive by land with the wind alone.

SECT. XIV.

OF THE PRESAGES OR PROGNOSTICS OF THE WINDS ; IN PROSECUTION OF THE FIFTEENTH ARTICLE

OF THE TABLE OF ENQUIRY.

TRANSITION.

THE more divination has been corrupted with vanity and superstition; the more the purer part

* Accounts and descriptions of this kind are to be met. with in voyages to the eastern countries; but how far they may be safely relied upon is not certain. And such kind

of it should be received and regarded. But natural divination is sometimes more, and sometimes less certain; according to the nature of the subject whereon it is exercised: so that in a subject of a constant and regular nature, it affords a true prediction; but in things of a various, compounded, and casual nature, one that is fallacious. And yet, even in a variable subject, predictions will generally hold true, if care be used in forming the rules; or not err greatly, though it should not hit upon the precise time of events. But even in point of time, some predictions will come very near; particularly such as are derived not from causes, but from the actual beginnings of things; though they manifest themselves sooner, in a prepared and well-disposed matter than otherwise. We now, therefore proceed to the prognostics of winds; wherewith we shall necessarily intermix some others, concerning rain and fair weather: which cannot well be separated from the former: but leave the particular enquiries about them to their own proper titles and history.

If the sun appear concave at its rising, the

of contrivances seem chiefly used in sandy deserts; the sand here in some measure answering to water; so as to make the motion a kind of sailing.

day will prove windy; or showery: if the concavity seem shallow, windy; but if deep, showery.

The sun rising pale, or, as we vulgarly express it, watery, denotes rain; and if it set pale, wind.

If the body of the sun set blood-red, it foretels great winds, for many days.

If, at sun-rising, his rays appear fiery, not yellow; it denotes rain rather than wind. Under

stand the same of his setting.

If, at the rising or setting of the sun, his rays appear contracted, or shortened, and do not shine out bright; though the weather be not cloudy; it denotes rain rather than wind.

If, before sun-rising, there appear over-early rays; it denotes both wind and rain.

If, at sun-rising, the sun throws his rays from the clouds, whilst one half of his body remains clouded; it foreshews rain; especially if those rays strike downwards, so as to shew the sun bearded: but if the rays break from the middle, or from several parts, whilst the sun's external face remains covered with clouds; it signifies great storms both of wind and rain.

If the rising sun be encompassed with a circle, wind may be expected from that quarter where the circle shall open; but if the whole circle shall vanish equably, it is a sign of fair weather.

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