|
|
Galileo Galilei Prima pagina |
||
|
Galileo Galilei CONCERNING THINGS WHICH FLOAT IN WATER OR MOVE IN IT Table of contents [interpolated by Mark A. Peterson, Mount Holyoke College] A new derivation, using moment Objections of Signor Buonamico Resistance to division, idea of atoms
TO THE GENTLE READERS AND COSIMO To satisfy the many who from Venice, Rome, and other places have asked me and continue to ask me for copies of this book, after it was sold out here in Florence, I have resolved to bring out a new edition, and I have so advised the Author; he, having seen by experience that some places in it were hard to understand for those less practiced in matters of geometry, has thought to facilitate the argument for them with the addition of some new material for greater clarity, without removing or altering anything in the first edition. You can be sure, gentle readers, that you have in this second printing the same that you had in the first, and more, the above mentioned additions, which are printed in a different font, so that they may be recognized immediately by all. May you live happily.
A DISCOURSE PRESENTED TO THE MOST SERENE DON COSIMO II, GRAND DUKE OF TUSCANY, CONCERNING BODIES WHICH FLOAT IN WATER OR MOVE IN IT, BY GALILEO GALILEI, PHILOSOPHER AND MATHEMATICIAN UNTO HIS MOST SERENE HIGHNESS. Translated from the Italian 2nd Edition by Thomas Salusbury, Esq., 1653 With modernization of the English by Mark Peterson, 2001
Considering, Most Serene Prince, that the publishing of this present Treatise, so different from what many expect, and so different from the intentions I announced in my Starry Messenger, might make some think that I had given up employment with the new Celestial Observations, or at least that I had handled them very remissly, I have judged it fit to render an account why I have postponed that and written this book instead. And first, my recent discoveries that Saturn is three-bodied, and that Venus has phases like the Moon, together with the consequences which follow from that, have not been so much the occasion of my delay as the investigation of the periods of revolution of each of the four Medicean Planets about Jupiter, which I determined in April of the year past, 1611, when I was in Rome; where, in the end, I ascertained that the first and nearest to Jupiter, moved about 8 degrees and 29 minutes of its sphere in an hour, making its whole revolution in one natural day and 18 hours, and almost a half. The second moves in its orb 4 degrees 13 minutes, or very near, in an hour, and its complete revolution requires 3 days 13 hours and one third, or thereabouts. The third passes in one hour 2 degrees 6 minutes of its circle, more or less, and passes the whole circle in 7 days 4 hours, or very near. The fourth, more remote than the rest, goes in one hour 0 degrees 54 minutes and almost one half, and finishes its revolution in 16 days and very nearly 18 hours. But because the excessive velocity of their returns requires a most scrupulous precision to calculate their positions in times past and future, especially if the time be for many months or years, I am therefore forced, with other observations, more exact than the former, and over a longer period of time, to correct the tables of such motions, and bring them to the highest accuracy: for such exactness my first observations do not suffice; not only because of the short interval of time, but because I had not then found a way to measure the distances between the said planets by any instrument: I observed such intervals with reference to the diameter of the body of Jupiter; taken, as I have said, by eye, which, though not admitting errors above a Minute, yet this does not suffice for the determination of the exact size of the spheres of those Stars. But now that I have hit upon a way of taking such measures with an error of scarcely a very few Seconds, I will continue the observation to the very occultation of Jupiter, which shall serve to bring us to the perfect knowledge of the motions and magnitudes of the orbes of the said Planets, together also with some other consequences thence arising. I add to these things the observation of some dark Spots, which are discovered in the Solar Body, which by their changing position suggests a remarkable thing, either that the Sun revolves in itself, or that perhaps there are other Stars, like Venus and Mercury, only visible when they are interposed between the Sun and our eye; or perhaps there is some truth in both ideas; the certainty of which things ought not to be scorned or belittled. Continual observation has assured me at last that these Spots are contiguous to the Body of the Sun, continually produced there in great number, and afterwards dissolved, some in a shorter, some in a longer time, and are carried about in a circle by the rotation of the Sun, which finishes its period in a Lunar Month or thereabouts, an accident great of itself, and greater for its consequences. Many causes have moved me to write the present Tract, the subject of which is the Dispute which I held some days ago with some learned men of this City, about which, as Your Highness knows, much has been said. The principal cause of my writing has been the intimation of your Highness, having commended Writing to me as the best means to make known true from false, real from apparent reasons, far better than by disputing noisily, where one, or other, or very often both disputants, through too great heat and raising of their voices, either are not understood, or else being carried away far from the first proposition by a show of stubborness, confuse both themselves and their audience with the novelty of their various proposals.
Moreover, it seemed to me appropriate to inform your Highness of the sequel of this controversy, as it has been repeatedly advertised by others already: and because the doctrine which I follow, in the discussion of the point in hand, is different from that of Aristotle, and interferes with his Principles, I have considered that it is far better to give my reasons in writing than by word of mouth against the authority of that most famous man, when many consider suspect everything that does not come from the Peripatetic School. And therefore I resolved to write the present Discourse: in which I hope to demonstrate that it was not out of capriciousness, or that I had not read or understood Aristotle, that I sometimes depart from his opinion, but because several reasons persuade me to it; and this same Aristotle has taught me to fix my judgment on Reason, and not on the bare Authority of the Master. And it is most certain according to the sentence of Alcinoos, that philosophizing should be free. Nor is the resolution of our question in my judgment without some general benefit, inasmuch as it may be of great help to know the truth, whether or not the shape of Solids is a cause of their sinking in water or not, in the building of bridges or other constructions on water, which often happens in affairs of great import.
I say therefore that being last summer in company with certain learned men, it was said in the argumentation that Condensation was the property of Cold, and there was alleged for instance, the example of ice. Now I at that time said that, in my judgment, the ice should rather be rarified water than condensed water, and my reason was because condensation leads to less volume and greater heaviness, and rarifaction results in greater lightness, and more volume; and water in freezing increases in volume, and the ice which is produced is lighter than the water on which it floats. |
|||
|
|
|
È manifesto quant'io dico... |
|
