The Nature Of Terrestrial Bodies

This Discourse 1 deals with the nature of terrestrial bodies [earth-ather] in general, as the foundtion for explaining the nature of exhalations [ionized air] and vapors.

The vapors rising from the seawater sometimes form salt above its surface.

Philosophers say that:

• such forms of these bodies are composed of elements by a perfect mixture
• bodies such as meteors are composed of elements by an imperfect mixture.

I will explain:

• the winds through the vapors through the air
• the clouds by the vapors gathering in some places
• the rain, hail, and snow by how those clouds dissolve

The particles of snow are shaped like small six-pointed stars, very perfectly arranged. These were not observed by the ancients. But it nonetheless is one of Nature’s rarest wonders.

I will also explain the tempests, thunder, lightning, and the various fires or lights that ignite in the air.

But above all, I will explain the rainbow and its colors so that one can also understand the nature of all those found in other subjects.

I will add the cause of:

• halos around the stars
• the multiple suns or moons that sometimes appear together.

The knowledge of these things depends on the general principles of Nature, which have not yet been well explained.

Therefore, I will have to start with some suppositions, as I did in the Dioptrics.

Cartesian Assumptions

Water, earth, air, and all other such bodies that surround us are composed of many small particles of various shapes and sizes.

• These have many gaps around them.

These gaps are not empty, but are filled with this very subtle matter* which also mediates the action of light.

Water is composed of small particles that are long, smooth, and slippery, like little eels.

• These join and intertwine.
• But they never tie or hook together that they cannot be easily separated.

Conversely, almost all those of earth as well as of air, and most other bodies, have very irregular and uneven shapes.

• They form hard bodies, like earth, wood, or similar substances if these are intertwined and catch and bind to each other, like how the branches of shrubs.
• They form physical oils or air if they are:
  • simply placed one on top of the other, without being much intertwined
  • so small that they can be moved and separated by the agitation of the air-aether around them.
    • This makes them:
      • occupy a lot of space
      • form liquid bodies, very decompressed and very light

The air-aether fills the gaps between the particles of these bodies.

It always move back and forth very quickly, not exactly at the same speed always and everywhere. It commonly moves

• a little faster at sea level than at the upper atmosphere
• faster near the equator than near the poles*
• in the same place faster in summer than in winter
• faster during the day than at night.**

This is because light is just luminous bodies pushing this fire-aether in all directions around them in a straight line, as was said in the Dioptrics.

Therefore, the sun’s rays, both direct and reflected, agitates the air-aether:

• more during the day than at night
• more in summer than in winter
• more near the equator than near the poles
• more against the earth than towards the clouds.

It follows that this fire-aether is composed of various very small particles. The largest particle has always the most force, just as large bodies have more force than the smaller ones when they are equally shaken.*

This means that the larger (less subtle) its particles are, the more it can agitate the particles of other bodies.

It is largest when and where it is most agitated such as:

• near the surface of the earth rather than towards the clouds
• near the equator rather than near the poles*
• in summer rather than in winter
• during the day rather than at night.

This is because the larger particles have more force.

• They can move more easily towards places where the agitation is greater.
• This makes it easier for them to continue their movement.

Nevertheless, there are always many very small particles that slip among these larger ones.