An entire body of philosophy according to the principles of the famous Renate Des Cartes in three books, (I) the institution ... (II) the history of nature ... (III) a dissertation of the want of sense and knowledge in brute animals ... / written originally in Latin by the learned Anthony Le Grand ; now carefully translated from the last corrections, alterations, and large additions of the author, never yet published ... by Richard Blome.

CHAP. III. Of Clouds and Mists.

I. How Clouds come to be poised in the Air. CLouds are suspended and poised in the Air, tho' they seem to be thick and heavy.

The Reason is, because the particles of Ice, or Snow, whereof they consist, are very small, and of much Surface, according to their bulk; and therefore are more hindred by the resistance of the Air from falling downwards, than they are driven down by their own weight; much like as a heavy loaden Ship is born up by the re∣sistance of the water that surrounds it. Besides, the winds that commonly blow near the Earth, consisting of a more thick and gross Matter, than those which are in the higher parts of the Air, are not only of force enough to stay and poise the Clouds in the Air; but also to raise them above that part of the Air wherein they are. Again, tho' the particles of Ice, being driven by the wind, do become contiguous to one another; yet are they not therefore closely joyned toge∣ther, but on the contrary do constitute a Body which is so loose, light, and diffused, that except heat do melt some of the parts of them, and by this means do condense and make them more heavy, they would never be able to fall to the ground.

II. VVhy there be more Mists in the Spring, than at other times. Mists are very frequent in the Spring, more than at other Seasons of the Year.

The Reason is, because at that time there is a greater Inequality between the heat of the Day and the cold of the Night; by which means it happens that a great quantity of Vapours do meet with the Coldness of the Air. For there are two things required to the turning of Vapours into Water or Ice: The first is, that their particles come so close together, that they may touch one another: The 2d is, that there be Cold enough to stop and unite them, when they are come thus close together. For the Cold would be of no use, if the particles of the Vapours were at a distance from one another, and separated. And their Con∣nexion would be of as little use, in case the agita∣tion of Heat were so great to hinder their union. And therefore when in the Spring, Vapours are car∣ried upwards by the heat of the Day, which by the cold of the following Night are again con∣densed, it cannot be otherwise, but that Mists must more frequently appear at that time, and the Earth be more abundantly moistned with them. And for the same Reason it is, that on the Sea-Coast, and in Marshy places, Mists are more fre∣quently generated than in Upland places, and such as are remote from the Sea; for the Water in those places sooner losing its heat, than the Earth, imparts a coldness to the Air, where afterwards the Vapours, that proceed in great abun∣dance from the hot and moist Earth, are con∣densed.

III. VVhat is the Cause why one Cloud seems to lie upon another. Sometimes a double range of Clouds appear in the Air, whereof the one is carried below the other.

The Reason is, because the Vapours, of which the Clouds are generated, do not with an equal force mount up into the Air, but some get up higher than others, before that they are sufficiently condensed for the forming of them. Whence it is, that we see some of them further from the Earth, and others nearer to it, and these too some∣times driven by different winds. Which is more especially perceived in Mountainous places, whe••e the sublimed Vapours are more unequally driv••n by the heat, than in other places. Hence it is, that according to the greater, lesser, or equal weight of the Cloud, the same Cloud doth either ascend, descend, or hang equally poised in the Air: As a Ship, according to her greater, less, or equal weight, doth rise higher, sink lower, or keep in an equal station in the water.

IV. The highest Clouds con∣sist of Icy particles. The highest Clouds are composed of particles of Ice, which may be gather'd from the Tops of the highest Mountains, which even in the midst of Summer are cover'd with Snow.

The Reason is, the great Coldness of that Region of the Air, which without doubt is colder, than that which lies upon the tops of the Mountains, or at least as cold; and because the Vapours, the higher they ascend, the more cold they meet with to condense them, and are the less liable to b•• pressed by the winds; therefore, for the most part, do the highest parts of the Clouds only consist of the thinnest Capillaments of Ice, situate at a great distance from one another.

V. VVhat is the Cause of the va∣rious Co∣lours of Clouds. Clouds appear of different Colours, sometimes black, at other times white, and sometimes are painted with all the Colours of the Rain-bow.

A Cloud appears black, when little or no Light is reflected from it, and then it is a sign of Rain; because the lower part of the Cloud is either alrea∣dy turned into water, or will be so suddenly. So on the other hand, when the Light is reflected from the Cloud, only by changing the Order of the Rays lighting upon the Cloud, without any other change of the Beams, then the Cloud appears white, and is a fore-runner of Fair-weather; be∣cause the said Cloud, consisting of distinct Globuli, or round particles, doth more readily vanish into the Air. And so lastly, when the Light is re∣flected from a Cloud in the same manner, as it is sent back from the Matter of a Rainbow; then that Cloud appears of many Colours, like a Rain∣bow, viz. Red, Green, and Purple, and may be a sign of Changeable-weather.

VI. VVhy Mists commonly arise about the Morn∣ing. Mists commonly are generated in the Morning, when a clear Night hath gone before, and when the weather is calm and free from the least Blast of wind. And if any one of these be wanting, either no Mists at all do arise, or if they do, they presently vanish.

The Reason is, because a Mist chiefly riseth from a Vapour, which breaks forth from the sur∣face of the Earth, being raised by a gentle heat, from Boggy places and Rivers, especially if they run slowly. Wherefore if the Heat be over∣great, it doth too much dilate the Vapours, and makes them fly upwards and vanish away. The extream sharpness of the Winter coldness, and great and violent winds, are also a hindrance to the production of Mists, because then the Vapour cannot be kept in by the ambient Cold, and the Thickness is lost, which is necessary to the consti∣tution of a Mist. Moreover, a Rainy or Cloudy Night, hinders it, because the Rain extinguisheth that warmth which is necessary for the raising of Exhalations. Lastly, When a Cloudy Night hath gone before, no Mist will ascend; for seeing that no Dew falls at that time, there is no matter for the raising of Vapours; and therefore it is necessary in order to the forming of a Mist above the ground, that the weather be still and calm, that the Earth be warm, and that a fair Night hath gone before.

VII. VVhy a Mist is dark and dusky. A Mist is dark and dusky, and deprives us of the Light of the Sun.

The Reason is, because a Body that consists of many particles so ranged, that the Light, by reason of the said parts lying one upon the top of another, is the less transmitted, the deeper it drives amongst these little Bodies; such a Body as this is, I say, tho' at first it be transparent, yet will at last, by this its swallowing up of the Light, become dark and dusky. For after this manner it is, that beaten Glass, foaming Waves, and a thick or close Wood become Dark or Dusky. And the same is the case with a Mist: For water attenuated into its least particles, which is a Vapour, and the Matter of a Mist, tho' with these its divided particles it be so tost up and down in the Air, that it scarcely hinders the strait course of the Light; yet when the said particles come together again, it constitutes some Drops, which tho' every one of them singly taken be transparent, do so receive the Light, that not so much as one of the beams is transmitted or passeth through the whole heap of them.

VIII. When a Mist is a sign of Rain. When a Mist having its parts united is carried downwards it threatens Rain; but if it be rarefi∣ed by degrees, and so ascend, it is a sign of fair Weather.

The Reason is, because when a Mist in an uni∣ted Body is carried upwards into the Air, it joyns to its self many particles of Dew, which are scat∣tered up and down the cold morning Air, which being soon after put into a motion by the least heat, are dissolved into Rain. Whence we ob∣serve that a Mist is often suddainly raised, where∣as the Sky before was very clear, and promised nothing less than Rain. For the heat agitating more forceably the little drops whereof the Mist doth consist, makes many of them to run toge∣ther, into such great drops, that the Air being no longer able to bear them up, they are forced to fall down in Rain.

IX. Great Mists and Clouds are gene∣rated by the meet∣ing of two Winds. When 2 or more Winds meet one another in their course, then Mists are formed in the place of their meeting.

The Reason is, because these Winds drive many vapors together to that place, which being united do either form Mists, if the Air therea∣bouts be very cold; or else produce Clouds, if the neighbouring Air be not cold enough to condense them, and so the matter of these Vapors mounting up higher into the Air, is there by the coldness of the place coagulated into Clouds. Yea, some∣times such a vast quantity of Vapors is gathered to∣gether in those places where 2 or more Winds meet, that the Winds cannot pass for them, nei∣ther above, nor under them, and so are forced to move round them, by which means they form a great Cloud of the said Misty matter, which be∣ing pressed on all sides by the Winds, gets a round and smooth surface.

X. A Mist magnifies and lessens Objects. If a man be look'd upon through a Mist, he appears like a Giant: Whereas the Sun being be∣held through it, appears much less.

The Reason is, because many Rays are refra∣cted in those drops, whereof the Mist doth con∣sist, which being gathered within the Eye, do dilate and extend the Object. But the Sun ap∣pears less, because the Beams proceeding from him, by reason of their great distance are dissipated, and do not all of them light upon the Eye; so that some of the lateral Rays are lost, which are wont chiefly to magnifie Objects.