Impact of the Sun, Moon, and Stars on the Winds

These general and regular winds would always be as I have just explained, if the surface of the earth were equally covered with water everywhere, or equally uncovered everywhere, so that there would be no diversity of seas, lands, and mountains, nor any other cause that could expand the vapors other than the presence of the sun, or condense them other than its absence.

When the sun shines, it causes more vapors to rise from the seas than from the lands because the lands do not provide as much material.

Conversely, when the sun is absent, the heat it has caused makes more vapors rise from the lands than from the seas, because it remains more strongly imprinted there.

This is why it is often observed along the seashore that the wind comes from the water during the day and from the land at night.

This is also why the lights called “St. Elmo’s fire” guide travelers toward the waters at night, as they follow the flow of the air, which draws toward the waters from the neighboring lands due to the condensation there.

The air touching the surface of the waters follows their course in some way, which is why the winds often change along the coasts of the sea with its ebb and flow; and why along large rivers, in calm weather, one can feel slight winds that follow their course.

The vapors rising from the waters are much more humid and thicker than those rising from the lands.

There is always much more air and exhalations among the latter. Hence, the same storms are usually more violent on the water than on land, and the same wind can be dry in one country and humid in another.

The south winds are humid almost everywhere. But they are dry in Egypt, where only the dry and burnt lands of the rest of Africa provide them with material.

This is why it almost never rains there. The north winds coming from the sea are humid. But because they are the coldest winds in Egypt, they cannot easily cause rain, as will be explained later.

Moonlight varies greatly depending on its distance from the sun. It contributes to the expansion of vapors, as does the light of other stars.

But this is only in proportion to how much we feel it affects our eyes, as these are the most certain judges we have to know the strength of the light.

Consequently, the light of the stars is hardly noticeable compared to that of the moon. Nor is the moon’s light compared to that of the sun.

Vapors rise very unevenly from different regions of the earth.

Mountains are heated by the stars in a different way than plains, forests differently than meadows, cultivated fields differently than deserts. Some lands are inherently warmer or easier to heat than others.

Consequently, very uneven clouds form in the air, which can be transported from one region to another by the slightest winds and can be sustained at various distances from the earth, often stacked above each other.

The stars act differently:

• on the higher clouds than on the lower ones
• on the lower ones compared to the earth beneath them
• on the same areas of the earth when there are no clouds covering them versus when there are.

After it has rained or snowed, the stars affect the earth differently than before.

This makes it almost impossible to predict the specific winds that will occur each day in each region of the earth, and there are often several contrary winds passing above each other.

However, one can generally determine which winds will be the most frequent and strongest, and in which places and seasons they will prevail, if one carefully considers all the factors noted here.

This can be even better determined in the great seas, especially in areas far from land, because there are no surface irregularities on the water like those we have observed on land, generating far fewer irregular winds, and those coming from the coasts can hardly reach there. This is evidenced by the experience of our sailors, who, for this reason, have named the largest sea the Pacific Ocean.

Almost all sudden changes in the air, such as it becoming warmer, rarer, or more humid than the season requires, depend on the winds—not only those in the regions where these changes occur but also those nearby and the various causes they proceed from.

For example, if we feel a south wind here, which, arising from a particular local cause and originating very nearby, does not bring much heat, and there is a north wind in neighboring countries coming from far away or from high up, the very subtle matter that this north wind brings with it can easily reach us and cause extraordinary cold.

This south wind, coming only from a nearby lake, can be very humid, whereas if it came from the deserted plains beyond, it would be drier.

And if it is caused only by the expansion of vapors from this lake, without the condensation of any others to the north contributing, it would make our air much thicker and heavier than if it were caused only by this condensation without any vapor expansion to the south.

Adding to this, the subtle matter and vapors in the pores of the earth, taking different courses, act like winds that bring with them exhalations of all kinds, according to the qualities of the lands they pass through. Moreover, as the clouds descend, they can cause a wind that drives the air from top to bottom, as I will explain later. I believe these account for all the causes of the changes in the air that are observed.

However, the various shapes of hail are neither curious nor remarkable compared to those of snow, which forms from these small ice knots or clusters arranged by the wind in the shape of leaves, as I have just described. When the heat begins to melt the small hairs of these leaves, it first melts those on the top and bottom because they are the most exposed to its action.

The small amount of liquid that emerges spreads over their surfaces, quickly filling the small irregularities found there, making them as flat and polished as those of liquid bodies. Despite this, the liquid freezes almost immediately, because if the heat is only strong enough to melt these small hairs surrounded by air, without melting anything further, it is not strong enough to prevent the material from refreezing when it is on these ice surfaces.

Afterward, this heat softens and bends the remaining small hairs around each knot in the circuit where it is surrounded by six other similar knots. It causes those hairs, which are farthest from the six neighboring knots, to bend and join with those opposite these six knots.

These hairs, being cooled by the proximity of the knots, cannot melt but, on the contrary, refreeze the material of the others as soon as it mixes with theirs.

This results in six points or rays forming around each knot, which can have various shapes depending on whether the knots are larger or smaller and more or less compressed, the hairs stronger or weaker and longer or shorter, the heat assembling them more or less slowly and moderately, and also depending on the strength of the wind accompanying this heat, if there is any wind.

Thus, the outer surface of the cloud, which was previously like what one sees around Z or M, subsequently becomes like what one sees around O or Q, and each ice particle composing it takes the shape of a finely carved small rose or star.