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them, manifest signs of burning and scorching, on the plains and plants they pass over; but for the business of fiery winds, which are a kind of blind lightning, or boiling air, without flame; it properly belongs to the enquiry of thunder and lightning.*

SECT. X.

OF THE THINGS CONTRIBUTING TO ORIGINAL WINDS; IN PURSUANCE OF THE TENTH ARTICLE OF THE

TABLE OF ENQUIRY.

TRANSITION.

WHAT the ancients have delivered upon the subject of winds, and their causes, is very confused, doubtful, and but seldom true. No wonder any one should not see clearly who stands remote. They speak as if the wind was something different from air in motion; as if exhalations generated, and made up the whole body of the winds; as if the matter of the winds were only a hot and dry exhalation; and lastly, as if the origin of the motion of the winds, was only a precipitation and percussion, from the cold of the middle region. All which are but arbitrary hy

* See more to this purpose in Mr. Bohun of Winds.

potheses, and creatures of the imagination; and yet, from such threads as these, they have wove large webs, in imitation of the spider. But to consult nature upon the point; 1. every impulse of the air makes a wind; 2. the exhalations mixed with the air, contribute more to the motion than to the matter of winds; 3. moist vapours are, by a proportionate heat, easier resolved into wind than dry exhalations; and, 4. numerous winds are generated in the lower region of the air; and many breathe out of the earth ; & besides those which are drove back, and thrown down from above.

We observed, under the article of General Winds, that the natural rotation of the air, without any other external cause, produces a perceptible wind within the tropics, where the air revolves in larger circles.

Next to this natural motion of the air, before we proceed to enquire concerning the sun, which is the principal parent of the winds; we must see whether any thing may, from clear experience, be attributed to the moon and the stars.

Great and strong winds rise some hours before an eclipse of the moon; so that if the moon be eclipsed at midnight, the winds blow the same evening but if the eclipse of the moon happen in the morning, they blow the midnight before.

Acosta observes, that in Peru, which is a very windy country, the winds blow most at the full

moon.

PRECEPT.

It well deserves to be observed, what effects the motions and changes of the moon have upon the winds; since they certainly have one upon the waters as for example, whether the winds are not somewhat more boisterous in the new and full-moon, than in the quarters; the tides being affected in the like manner. For although it may seem a commodious hypothesis, that the moon rules over the waters; but the sun and stars over the air; yet it is certain, that water and air are very homogeneous bodies; and that, next to the sun, the moon has here the greatest power below.

It is observed, that the greatest winds blow about the time of the conjunctions of the pla-.

nets.

Storms and tempests frequently happen at the rising of Orion: but it must be here examined, whether this happens not because that constellation rises at the time of year most disposed to produce winds; so as rather to be a concomitant than a cause. And the same question may justly be put, as to the rising of the Pleiades,

with regard to showers; and of Arcturus, with regard to storms*. And so much for the moon and stars.

Doubtless the sun is the primary efficient of many winds; as operating by his heat upon two kinds of matter; viz. the body of the air, and upon vapours and exhalations.

The sun, when powerful, expands even pure air; perhaps a third part of which is considerable: whence, by simple expansion, some breeze must necessarily arise in the path of the sun; especially in the times of greatest heat: and this rather two or three hours after the sun is up, than in the first of the morningt.

In Europe, the nights are sultry; but in Peru, the three first hours of the morning: and both for the same reason; viz. because the winds and breezes cease at those hours.

In a water-thermometer, the dilated air depresses the water, as if it were by a blast; but in a glass filled only with air, and capt with a bladder, the air, when dilated, blows up the bladder, like a manifest wind.

* It will come to be considered, whether the rising of the constellations here mentioned, be meant of their cosmical or acronical risings; and whether the signs of this kind are not rather poetical than natural.

t See Dr. Jurin's Appendix to Varenius.

F

We made an experiment of this kind of wind, in a round turret, close shut up on all sides; by placing in the midst thereof a chafing-dish of coals, thoroughly ignited, to prevent their smoaking. On one side of the chafing-dish at some distance, we suspended a thread furnished with a cross of feathers, that it might be the more susceptible of motion; and now, when the heat was increased, and the air expanded, the feather-cross with its string, appeared to be agitated, and moved about various ways: then making a hole in the window of the turret, there issued out a warm exhalation; not in a continued stream, but by fits in an undulating manner.

So, likewise, the condensation of the air by cold after having been dilated, creates the same kind of wind, though weaker, by reason of the lesser force of the cold. And hence, in Peru, there is not only a greater coolness perceived under every little shade than here with us; but also a manifest breeze, from the shrinking and contracting of the air, when it enters the shade. And thus much for wind caused by a mere dilatation, and contraction of the air.

The winds proceeding from the mere motions of the air without any mixture of vapour, are soft and gentle. We must next examine into the vaporous winds, or those produced from vapour; which may prove as much stronger than

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