I am of opinion then that every Sun is surrounded with a Whirl-pool or Vortex of Matter in a very swift Motion; tho not in the least like Cartes’s either in their bulk, or manner of Motion. For Cartes makes his so large, as everyone of them to touch all the others round them, in a flat Surface, just as you have seen the Bladders that Boys blow up in Soap-suds do: and would have the whole Vortex to move round the same way. But the Angles of every Vortex will be no small hindrance to such a Motion. Then the whole matter moving round at once, upon the Axis as it were of a Cylinder, did not a little puzzle him in giving Reasons for the Roundness of the Sun: which however they may satisfy some People that do not consider them, really prove nothing of the matter. In this æthereal matter the Planets float, and are carry’d round by its motion: and the thing that keeps them in their own Orbs is, that they themselves, and the matter in which they swim. equally strive to fly out from the Center of this Motion. Against all which there are many Astronomical Objections, some of which I touch’d upon in my Essay of the Causes of Gravity. Where I gave another account of the Planets not deserting their own Orbs; which is their Gravitation towards the Sun. I show’d there the Causes of that Gravitation, and cannot but wonder that Cartes, the first man that ever began to talk reasonably of that matter, should never meddle with, or light on it. Plutarch in his Book of the Moon above mentioned says, that some of the Antients were of opinion, that the reason of the Moon’s keeping her Orbit was, that the force of her Circular Motion was exactly equal to her Gravity, the one of which pull’d her to, as much as the Other forc’d her off from the Centre. And in our Age Alphonsus Borellus, who was of this same opinion in the other Planets as well as the Moon, makes the Gravitation of the primary Planets to be towards the Sun, as that of the secondary is towards the Planets round which they move: Which Mr. Isaac Newton has more fully explained, with a great deal of pains and subtilty; and how from that cause proceeds the Ellipticity of the Orbs of the Planets, found out by Kepler. According to my Notion of the Gravitation of the Planets to the Sun, the matter of his Vortex must not all move the same way, but after such a manner as to have its parts carry’d different ways on all sides. And yet there is no fear of its being destroy’d by such an irregular motion, because the æther round it, which is at rest, keeps the parts of it from flying out. With the help of such a Vortex as this I have pretended in that Essay to explain the Gravity of Bodies on this Earth, and all the effects of it. And I suppose there may be the same cause as well of the Gravitation of the Planers, and of our Earth among the rest, towards the Sun, as of their Roundness: a thing so very hard to give an account of in Cartes’s System.
I must differ from him too in the bigness of the Vortices, for I cannot allow them to be so large as he would make them. I would have them dispers’d all about the immense space, like so many little Whirl-pools of Water, that one makes by the stirring of a stick in any large Pond or River, a great way distant from one another. And as their motions do not all intermix or communicate with one another; so in my opinion must the Vortices of Stars be plac’d as not to hinder one anothers free Circumrotations.
So that we may be secure, and never fear that they will swallow up or destroy one another; for that was a mere fancy of Cartes’s; when he was showing how a fix’d Star or Sun might be turn’d into a Planet. And ’tis plain, that when he writ it, he had no thoughts of the immense distance of the Stars from one another; particularly, by this one thing, that he would have a Comet as soon as ever it comes into our Vortex, to be seen by us. Which is as absurd as can be. For how could a Star, which gives us such a vast Light only from the Reflection of the Beams of the Sun, as he himself owns they do; how I say could that be so plainly seen at a distance ten thousand times larger than the Diameter of the Earth’s Orbit? He could not but know that all round the Sun there is a vast Extensum; so vast, that in Copernicus’s System the magnus Orbis is counted but a point in comparison with it. But indeed all the whole story of Comets and Planets, and the Production of the World, is founded upon such poor and trifling grounds, that I have often wonder’d how an ingenious man could spend all that pains in making such fancies hang together. For my part, I shall be very well contented, and shall count I have done a great matter, if I can but come to any knowleg[d]e of the nature of things, as they now are, never troubling my head about their beginning, or how they were made, knowing that to be out of the reach of human Knowle[d]ge, or even Conjecture.--C. Huygens, Cosmotheoros. "Every Sun has a Vortex round it, very different from those of Cartes"
The long quoted passage is the concluding section of Huygens's posthumous Cosmotheoros. I have quoted (and discussed) it before (recall here). It is notable that the book closes with a frontal attack on Descartes's cosmology and cosmogony. These are trifling fancies. Huygens introduces his own book as "fancy," but his is founded on probabilities (and analogies).Scholars sometimes call Huygens a 'Cartesian;' despite their shared commitment to mechanical philosophy, that was always problematic because Huygens's early work on Saturn reveals a platonizing sensibility absent in Descartes. But this late work reveals he is clearly a disillusioned Cartesian (recall also yesterday's biting criticisms of Descartes's account of animals).
As an aside, the paragraph may also be a subtle dig at Isaac Newton. For the first edition of the Principia (the only one Huygens would have read) closes with some cosmological and cosmogenic speculations about the role of comet in the economy of life in the universe. It's not that Huygens can be against some such speculation, but perhaps he thought it inappropriate for a work in mathematical natural philosophy.
It is also notable that this closing paragraph is the first and only explicit mention of Newton (there is one earlier allusion) in the whole book. Huygens here is, in fact, rejecting two features of Newton's physics: the law of universal gravity. That is, (i) Huygens is limiting the inverse square law to the bodies of the solar system. (With George Smith, I have explained his empirical argument for doing so.) And (ii) Huygens is rejecting Newton's implicit constraints on any explanation of the cause of gravity--for Huygens bodies are not centers of attraction. And so in Huygens's account of the mechanism of the cause of gravity (something Newton claimed to be agnostic about) the Sun plays no role (see his treatment in the Discourse on Gravity).+ A key background claim for (ii) is spelled out in the Cosmotheoros: (iii) Huygens introduces a fixed ether that fully surrounds the solar system, and each solar system, to keep the system of vertices of each solar system in place.
This ether has three important properties: (iv) it is strong enough to keep the system of vertices of each solar system in place; (v) the ability to absorb energy in such a way such as (v*) to prevent causal interaction among the motions of each solar system; while (vi) to allow light waves to be transmitted among solar systems. To the best of my knowledge Huygens does not investigate these properties of this ether. (But it would be worth looking at his papers.) In particular, (iv-v) imply that (vii) this ether must have non-negligible mass and so (vii*) Huygens's (quasi) universal ether is different in character than the ether Newton toys with in the Opticks in order to explain universal gravity. Newton's ether has negligible mass (and so is causally trivial).
There are two very interesting consequence of Huygens's way of conceiving things, the first one he is explicit about the second one not: (viii) even if the motions of the planets are not themselves in stable equilibrium (they are "irregular"), each solar system is in equilibrium due to the universal ether that keeps it in place ("never fear that they will swallow up or destroy one another"). As Huygens hints this result cannot be assured in Newton's system (without Divine intervention). (ix) Each solar system may have its own gravitational laws that reflect the stable equilibrium of its system of vertices (held in place by the universal ether). While the physics of this is un-Newtonian, in Book I of the Principia, Newton had actually provided the series of gravitational models (with different force laws) that could have given Huygens the thought.
Now, let's grant Huygens the properties of his universal ether. And I ignore interesting questions about the relative motions, if any, among each solar system. (Huygens seems to be implying that the universal ether is at rest or moving uniformly.) Some other time I wish to return to my discussion about simultaneity in Huygens (and Newton). But here I close by calling attention to the following: (x) there is a tension between (v*) and (vi). For, how can each solar system be causally isolated yet somehow allow the transmission of light among them? This would make light, as it were, causally epiphenomenal. The problem does not go away by pointing to the wave theory of light.++ While light is propagated in waves, for Huygens (xi) light is itself matter in motion.+++ So, from (xi) and (vi) it follows that (xii) even solar systems separated by the ether cannot really be causally isolated because matter is exchanged among them through light.++++
+Huygens also has a lovely experiment to argue for this claim.
++ One may be tempted to go speculative, and bite the bullet on Huygens's behalf and suggest that light waves function in the manner that Jonathan Bennett imagines a Spinozistic field metaphysic operates. But as I explain in the body of the text, the historical Huygens can't avail himself to that speculation.
+++That is there is a gap between Huygens's mechanical conception of life and his wave theory. He recognized this gap, and it is worth quoting Huygens in full:
Then if we consider the wonderful nature of Light, and the amazing Artifice in the fit framing the eye for the reception of it, we cannot but see that Bodies so vastly remote could not be view’d by us in their proper Figures and just Distances, any other way than by Sight. For this Sense, and all others that we know of, must proceed from an external Motion. Which in the sense of Seeing must come either from the Sun, the fixt Stars, or Fire: whose Particles being whirled about with a rapid Motion, communicate it to the Celestial Matter about, whence ’tis convey’d in an instant to the most distant parts, just like Sound through the Air. If it were not for this Motion of the intermediate Matter, we should be all in darkness, and have sight neither of Sun nor Stars, nor any thing else, for all other Light must come to us at second-hand from them. This Motion perceived by the Eyes is called Light. And the nice Curiosity of this Perception is admirable, in that it is caused by the smallest Particle of that fine Matter, and can at the same time determine the Coast from whence the Motion comes; in that all these different Roads of Motion, these Waves crossing and interfering with one another, are yet no hindrance to every ones free passage. All these things are so wisely, so wonderfully contrived, that it’s above the power of humane Wit, not to invent or frame somewhat like them, but even to imagine and comprehend them. For what can be more amazing, than that a Particle of Body should be so devised and framed, as by its means to show us the Shape, the Position, the Distance, and all the Motions, nay and all the Colours, distinguishing of a Body that is far remote from us? And then the artful Composition of the Eye, drawing an exact Picture of the Objects without it, upon the concave side of the Choroides, is even above all admiration, nor is there any thing in which God has more plainly manifested his excellent Geometry. And these things are not only contrived and framed with so great Wisdom and Skill, as not to admit of better, but to any one that considers them attentively, they seem to be of such a nature as not to allow any other Method. For it’s impossible that Light should represent Objects to us at so vast a distance, except by such an intervening Motion; and it’s as impossible that any other Composition of the Eye should be equally fitted to the reception of such Impressions.
One important qualification: Huygens knows that the speed of light is finite. (He had been actively involved in Romer's determination of its speed.)
++++I thank Marius Stan for discussion.