Introduction to Astronomy

...knowledge of all things to those standing around. Indeed, the first question asked is whether the subject of the inquiry has been discovered or not. The second is what it is. The third is what kind it is. The fourth is why. Therefore, the first origin of every discovery lies in the senses; for the senses move toward opinion. From there, an ascent is made to reason through what is called the intellect. Thus, as we have taught, the first cause of the discovery of astrology original: "astrologie"; here referring to the general study of the stars, including what we now call astronomy was sight. Second, reason followed, so that from this point the perfection of the art might ascend to a certain other understanding of the celestial secret.

¶ All authority of philosophy original: "phie" / "philosophie" and of heavenly investigation agrees that the substance of the stellar bodies is neither created from any of the elements of this world, nor composed of several or all of them. For if they were made of these elements, the necessities of elementary offspring would follow: generation, corruption, increase, decrease, resolution, and other alterations of that kind. Since these things are foreign to that place, reason concludes that the substance of both the celestial circles and the stellar bodies consists of a certain fifth nature The "quintessence" or aether, believed to be incorruptible unlike the four earthly elements.

¶ Furthermore, the quality of those bodies lies in their form. For they are spherical, translucent bodies living by a natural motion. We understand the necessary cause of these motions to be that the motion of the higher essences might mix the lower natures by acting upon them. This commingling was necessary for all generation. Whence the philosopher finally understood that the lower world is bound by a certain necessity to the higher world; he who willed it by a certain natural motion, draws this world along as he holds it. For the world of the higher things, perpetually surrounding the lower things, draws what is bound to it, and by agitating the materials of the world's motion, it mixes acts and passions, the causes of all generations.

¶ Moreover, no motion but the circular was fit for the celestial bodies. For no motion is perfect except the circular, which, since it lacks a beginning and an end, admits no rest in any part. For other motions, since they have a beginning and an end, must necessarily stop when they arrive there.

¶ However, there are two motions of the bodies of the lower world: one is straight, having an end where they stop when they are led through, such as fire and air moving upward, and earth and water moving downward. The other is circular, which drives resolutions and alterations from one thing into another, and again from those back into this. Thus, the motion of the surrounding world, drawing this motion along, acts upon the generations and corruptions of things. For generations exist in the elements potentially original: "potentialiter"—that is, in potential—while resolution actually restores the birth from one thing into another. For example: in wood, smoke is present in potential, which fire, acting upon the wood, generates in the act original: "actu" itself. Or otherwise: generation and corruption are in the elements in potential, which the motion of the stars produces into the thing itself by altering the elements and resolving them into one another.

The action of one body upon another in all things of this world is found to be two-fold: either by the contact of both, or by something mediating between the two. By contact, indeed, as fire causes burning in matter. By the mediation of another, it is three-fold. First, by will, as when one moves another through a medium touching both extremes at once, or interceding between both. Second, by nature, as when fire makes water hot by means of heat. Third, by a certain intrinsic property: as, for example, the magnet stone original: "lapis magnes" draws iron through the intervening space of air; because the power of acting is in the stone, and the nature of the iron is passive to that action. This nonetheless happens even if another body is interposed, such as a copper plate or something of that kind; but it also happens by contact when the stone...