Descartes' System of Astronomy

September 24, 2022

Descartes was the first who tried to ascertain precisely this invisible chain that Kepler said to link the planets to the sun.

He explained that the real inertness of matter was=

  • not in an aversion to motion and
  • not in a propensity to rest

The real inertness of matter was in a power=

  • of continuing indifferently either at rest or in motion, and
  • of resisting, with a certain force, whatever tried to change its state from the one to the other

All of space was full of aether. This aether and space were the same. Consequently, there was no void.

This immense aether was divided into an infinite number of very small cubes which whirled around on their own centers to create two different elements=

  1. The angular parts

These were rubbed off and grinded yet smaller by their mutual friction. This was the most subtile and moveable part of the aether

  1. The little globules

These were formed by the rubbing off of the first. The gaps between these globules was filled up by the angular parts.

The infinite space filled with the aether caused infinite collisions which caused the little globules to be grinded down into the angular parts. This caused the angular parts to be more than enough to fill the gaps between the little globules, and became heaped up together, without any mixture of the little globules along with it.

This was the original division of the aether.

Descartes’ Law of Conservation of Energy

A certain amount of motion was originally impressed by the Creator and the laws of motion were so adjusted as always to preserve the same amount in it, without increase nor reduction.

Whatever motion was lost by one part of the aether was communicated to some other*. Whatever was acquired by one part of the aethre, was derived from some other.

*Translator’s note= This is now the law of conservation of energy

Thus, through an eternal revolution from rest to motion and motion to rest, the amount of motion in the whole was always the same.

But there was no void. And so a movement of one part of the aether moved another part out of its place, which led to a chain reaction.

To avoid an infinite progress, a body that pushed away the aether in front of it would have the aether roll in immediately behind it to supply the place of the aether that was displaced.

This is similar to the swimming of a fish. The water, which it pushes before it, immediately rolls backwards, to supply the place of what flows in. The water thus forms a small circle or vortex around the fish.

In the same way, the motion originally impressed by the Creator on the aether necessarily produced in it an infinity of large and small vortices, or circular streams.

The law of motion always adjusted to preserve the same amount of motion in the universe. This made those vortices either continued forever, or by their dissolution, give birth to others of the same kind.

There was, thus, at all times an infinite number of bigger and smaller vortices or circular streams revolving in the universe.

But whatever moves in a circle is constantly trying to fly off from the center of its revolution because the natural motion of all bodies is in a straight line.

All the bodies in each of those greater vortices were thus continually pressing from the center to the circumference according to their bulk and solidity.

  • The larger and more solid globules of the second element forced themselves upwards to the circumference
  • The smaller, more yielding, and more active particles of the first were forced downwards to the center as these could flow even through the gaps of the second

Despite their natural tendency to go to the circumference, they were forced to the center for the same reason that wood floats when plunged in water. This is because its tendency downwards is weaker than that of the particles of water which force it upwards.

But the angular parts were in excess of what was needed to fill in the gaps between the second. It necessarily accumulated in the center of each of these great circular streams, and formed there the firey and active substance of the Sun.

The Solar Systems were infinite in number. Each Fixed Star was the center of one.

Descartes is among the first of the moderns who took away the boundaries of the Universe.

  • Even Copernicus and Kepler confined it within, what they supposed, the vault of the Firmament.

The center of each vortex was thus occupied by the most active and moveable parts of the aether. There was necessarily among them, a more violent agitation at the center than in any other part of the vortex which then supported the movement of the whole.

The Third Element

But, among the particles of the first element, which fill up the interstices of the second, there are many, which, from the pressure of the globules on all sides of them, necessarily receive an angular form, and thus constitute a third element of particles less fit for motion than those of the other two.

The particles of this third element were formed in the interstices of the second. They thus are necessarily smaller than those of the second and are urged down towards the center, along with those of the first.

In the center, when a number of them happen to take hold of one another, they form such spots upon the surface of the accumulated particles of the first element, as are often discovered by telescopes upon the face of that Sun, which enlightens and animates our particular system.

Those spots are often broken and dispelled, by the violent agitation of the particles of the first element, as has hitherto happily been the case with those which have successively been formed upon the face of our Sun.

Sometimes, however, they encrust the whole surface of that fire which is accumulated in the center.

The communication between the most active and the most inert parts of the vortex being thus interrupted, the rapidity of its motion immediately begins to languish, and can no longer defend it from being swallowed up and carried away by the superior violence of some other like circular stream; and in this manner, what was once a Sun, becomes a Planet.

Thus, the time was when the Moon was a body of the same kind with the Sun, the firey center of a circular stream of ether, which flowed continually round her; but her face having been crusted over by a congeries of angular particles, the motion of this circular stream began to languish, and could no longer defend itself from being absorbed by the more violent vortex of the Earth, which was then, too, a Sun, and which chanced to be placed in its neighbourhood. The Moon, therefore, became a Planet, and revolved round the Earth.

In the process of time, the fate of the moon also befell on the Earth. Its face was encrusted by a gross and inactive substance. The motion of its vortex began to languish, and it was absorbed by the greater vortex of the Sun= but though the vortex of the Earth had thus become languid, it still had force enough to occasion both the diurnal revolution of the Earth, and the monthly motion of the Moon.

For a small circular stream may easily be conceived as flowing round the body of the Earth, at the same time that it is carried along by that great ocean of ether which is continually revolving round the Sun; in the same manner, as in a great whirlpool of water, one may often see several small whirlpools, which revolve round centers of their own, and at the same time are carried round the center of the great one.

Such was the cause of the original formation and consequent motions of the Planetary System.

When a solid body is turned round its center, those parts of it, which are nearest, and those which are remotest from the center, complete their revolutions in one and the same time. But it is otherwise with the revolutions of a fluid= the parts of it which are nearest the center complete their revolutions in a shorter time, than those which are remoter.

The Planets, therefore, were all floating in that immense tide of ether which is continually setting in from west to east round the body of the Sun, complete their revolutions in a longer or a shorter time, according to their nearness or distance from it.

To Descartes, there was no exact proportion observed between the times of their revolutions and their distances from the center.

For that nice analogy, which Kepler had discovered between them, having not yet been confirmed by the observations of Cassini, was, as I before took notice, entirely disregarded by Descartes.

According to him, their orbits might not be perfectly circular, but be longer the one way than the other, and thus approach to an Ellipse.

Nor yet was it necessary to suppose, that they described this figure with geometrical accuracy, or even that they described always precisely the same figure. It rarely happens, that nature can be mathematically exact with regard to the figure of the objects she produces, upon account of the infinite combinations of impulses, which must conspire to the production of each of her effects.

No two Planets, no two animals of the same kind, have exactly the same figure, nor is that of any one of them perfectly regular. It was in vain, therefore, that astronomers laboured to find that perfect constancy and regularity in the motions of the heavenly bodies, which is to be found in no other parts of nature. These motions, like all others, must either languish or be accelerated, according as the cause which produces them, the revolution of the vortex of the Sun, either languishes, or is accelerated; and there are innumerable events which may occasion either the one or the other of those changes.

It was thus, that Descartes endeavoured to render familiar to the imagination, the greatest difficulty in the Copernican system, the rapid motion of the enormous bodies of the Planets.

When the fancy had thus been taught to conceive them as floating in an immense ocean of ether, it was quite agreeable to conceive that they should follow the stream of this ocean, how rapid soever. This was an order of succession to which it had been long accustomed, and with which it was, therefore, quite familiar.

The motions of the Heavens was connected with a vast immense system, which joined together a greater number of the most discordant phaenomena of nature, than had been united by any other hypothesis

It was a system in which the principles of connection, though perhaps equally imaginary, were, however, more distinct and determinate, than any that had been known before; and which attempted to trace to the imagination, not only the order of succession by which the heavenly bodies were moved, but that by which they, and almost all other natural objects, had originally been produced.

The Cartesian philosophy is now almost universally rejected, and the Copernican system us universally received.

Yet, it is not easy to imagine, how much probability and coherence this admired system was long supposed to derive from that exploded hypothesis.

Before Descartes had published his principles, no one really heartily embraced the disjointed and incoherent system of Tycho Brahe. But it was constantly talked of by all the learned as being probable and upon a level with that of Copernicus.

They took notice of its inferiority with regard to coherence and connection, expressing hopes, however, that these defects might be remedied by some future improvements.

But when the world beheld that complete, and almost perfect coherence, which the philosophy of Descartes bestowed on Copernicus’s system, the imaginations of mankind could no longer refuse themselves the pleasure of going along with so harmonious an account of things.

The system of Tycho Brahe was every day less and less talked of until it was forgotten altogether.

The system of Descartes connected the real motions of the heavenly bodies according to the system of Copernicus only when considered in the large scale but not in the small scale.

Descartes never himself observed the Heavens with any particular application. He was not ignorant of the observations made before his time, but he seems to have paid them no great attention. This probably came from his own inexperience in the study of Astronomy.

He was content with observing that perfect uniformity could not be expected in their motions. He did not solve all the minute irregularities which Kepler found in the movements of the Planets. Instead, he showed that irregularities might happen from the nature of the causes which produced them. A great number of successive revolutions lead to other kinds of irregularities. This relieved him from needing to apply his system onto the observations of Kepler and the other Astronomers.