Clouds

Vapor Transparency

Vapors cause:

• winds by expanding
• clouds and fogs by condensing and contracting

Vapors are called:

• fogs if they are significantly less transparent than pure air and extend to the earth’s surface
• clouds if they remain suspended higher up

They become less transparent than pure air because:

• their movement slows down
• their particles are close enough to touch each other

They join and gather into various small clusters, which are water droplets or ice particles.

As long as they remain completely separate while floating in the air, they cannot obstruct the passage of light.

But when they are assembled, the surface of each water drop or ice reflects part of the rays that strike them.

• These surfaces easily become numerous enough to reflect almost all the rays.

Droplets

Water droplets form when the air-aether around the small vapor particles no longer has enough force to make them expand and repel each other, but still can make them fold and subsequently join and accumulate into a sphere.

The surface of this sphere becomes immediately smooth and polished because:

• the particles of the air that touch it move differently from its own particles
• the air-aether in its pores moves differently from that in the pores of the air, as explained about the surface of seawater.

This is why the droplets also become perfectly round. River water swirls and forms circles where something prevents it from moving straight.

Similarly, the air-aether flows through the pores of other bodies, in the same way as a river flows through the spaces between the plants growing in its bed.

• It moves more freely from air to air and water to water, than from air to water or water to air.

It must swirl inside the water droplet and also outside in the surrounding air.

• But it swirls in a different manner inside than outside, thus arranging all the particles of its surface in a circle.

The water, being a liquid body, must obey these movements.

This explains why water droplets must be perfectly round, in the sense that their sections are parallel to the earth’s surface;

Its circumference is equidistant to its center since they are equally pressed by the surrounding air-aether on all sides, assuming that the air-aether is calm and still, as we must suppose here.

When the drops are so small, their weight is not enough to force them to divide the air and fall.

This makes them flatter and less thick in their height than in their width, like T or V.

They have air around their sides as well as underneath.

If their weight is not enough to make the air below them give way and let them fall, then it is equally not enough to make the air on their sides move aside and let them become wider.

When their weight makes them descend, the air they divide does not make them somewhat longer and narrower, like X or Y.

Being surrounded all around, the air they displace as they fall must rise above them to fill the space they leave.

It can only do so by flowing along their surface, where it finds a shorter and easier path when they are round than if they had any other shape.

Of all shapes, the round shape is the most efficient. It has the least surface area relative to its volume.

Therefore, these droplets must always remain round, unless the force of some wind or some other specific cause prevents them.

Their size depends on how close the particles of the vapor are to each other when they begin to form the droplets, as well as on how agitated they are afterward, and on the amount of other vapors that can join them.

Initially, each droplet is composed of only two or three small parts of the vapor that meet.

But soon after, if this vapor is somewhat thick, two or three of the droplets that have formed from it will meet and join into one, and again two or three of these will join into one, and so on, until they can no longer meet.

While they are suspended in the air, other vapors can also join them and increase their size until, finally, their weight causes them to fall as rain or dew.

Ice Particles

Ice particles form when the cold is so intense that the vapor particles cannot be folded by the fire-aether among them.

If this cold sets in after the droplets are already formed, it freezes them all round unless accompanied by a strong wind.

• This may flatten them slightly on the side it hits.

Conversely, if the cold sets in before they begin to form, the parts of the vapor only join lengthwise.

• This creates fine ice filaments.

Most commonly, the cold arrives between these 2 stages.

• It freezes the vapor particles as they fold and pile up, without giving them time to join perfectly to form droplets.

Thus, it creates small knots or clusters of ice.

• These appear white because they are composed of many filaments that remain separated and have distinct surfaces, even though they are folded over one another.

These knots appear fuzzy or hairy all around because there are always several particles of the vapor that are unable to fold and pile up as quickly as the others.

• This causes them to attach straight against them, forming the tiny hairs that cover them.

These knots form larger or smaller, and the filaments that surround them are thicker and shorter, or finer and longer depending on whether:

• the cold arrives gradually or suddenly
• the vapor is dense or sparse

Vapors Converting to Water or Ice

There are always 2 things required to convert vapors into water or ice:

1. Their particles are close enough to touch each other
2. There is enough cold around them to make them join and stay together when they touch.

It would not be enough for the cold to be very great if the vapors were spread so far apart in the air that they did not touch at all, nor would it be enough for them to be very close and compressed if their heat, that is, their agitation, were strong enough to prevent them from joining.

Thus, clouds do not always form high in the air, even though the cold is always sufficient for this effect.

It also requires:

• a westerly wind, opposing the usual course of the vapors, to gather and condense them where it ends; or
• 2 or more other winds, coming from different directions, to press and accumulate them between them; or
• one of these winds drives them against a cloud already formed; or
• they gather against the underside of a cloud as they rise from the earth.

Fog forms only when the cold air and the abundance of vapors coincide.

This often happens in the evening or at night after a warm day, especially in spring more than other seasons, and even more than in autumn. This is because the temperature difference between day and night is greater.

Fog forms more often in marshy or coastal areas than in places far from water or on water far from land. This is because water cools faster than land, chilling the air, which condenses the vapors produced abundantly by warm, moist land.

The largest fogs, like clouds, form where the course of two or more winds ends.

These winds drive many vapors to these locations, where they thicken into fog if the air near the ground is very cold or into clouds if it is only cold enough to condense them higher up.

Note that the water droplets or ice particles that make up fog must be very small; if they were even slightly larger, their weight would quickly cause them to fall to the ground, so we would not call it fog but rain or snow.

There can never be any wind where fog forms, as it would quickly disperse it, especially when composed of water droplets. Even the slightest air movement causes these droplets to join and grow larger, eventually falling as rain or dew.