The Sidereal Messenger of Galileo Galilei

The Sidereal Messenger of Galileo Galilei - and a Part of the Preface to Kepler's Dioptrics Containing the Original Account of Galileo's Astronomical Discoveries

Kepler remarks on the importance of the application of the telescope to astronomical investigations as indicated by Galileos discoveries, published in his Sidereal Messenger. The Sidereal Messenger of Galileo has been for a long time in everybodys hands, also my Discussion, such as it is, with this Messenger, and my Brief Narrative in confirmation of Galileos Sidereal Messenger, so any reader may briefly weigh the chief points of that Messenger and see the nature and the value of the discoveries made by the aid of the telescope, the theory of which I am intending to demonstrate in this treatise. Actual sight testified that there is a certain bright heavenly body which we call the Moon. It was demonstrated from the laws of optics that this body is round; also Astronomy, by[80] some arguments founded upon optics, had built up the conclusion that its distance from the earth is about sixty semi-diameters of the earth. Various spots showed themselves in that body; and the result was a dubious opinion among a few philosophers, derived from Hecatus account of the stories about the island of the Hyperboreans,19 that the reflected images of mountains and valleys, sea and land, were seen there; but now the telescope places all these matters before our eyes in such a way that he must be an intellectual coward who, while enjoying such a view, still thinks that the matter is open to doubt. Nothing is more certain than that the southern parts of the moon teem with mountains, very many in number, and vast in size; and that the northern parts, inasmuch as they are lower, receive in most extensive lakes the water flowing down from the south. The conclusions which previously Pena published as disclosed by the aid of optics, started indeed from certain slight supports, rather than foundations, afforded by actual sight, but were proved by long arguments depending one upon another, so that they might be assigned to human reason rather than to sight; but now our very eyes, as if a new door of heaven had been opened, are led to the view of matters once hidden from them. But if it should please any one to exhaust the force of reason[81]ing upon these new observations, who does not see how far the contemplation of nature will extend her boundaries, when we ask, What is the use of the tracts of mountains and valleys, and the very wide expanse of seas in the moon? and May not some creature less noble than man be imagined such as might inhabit those tracts? With no less certainty also do we decide by the use of this instrument even that famous question, which, coeval with philosophy itself, is disputed to this day by the noblest intellectsI mean, whether the earth can move (as the theory of the Planets greatly requires) without the overthrow of all bodies that have weight, or the confusion of the motion of the elements? For if the earth were banished from the centre of the universe, some fear lest the water should leave the orb of the earth and flow to the centre of the universe; and yet we see that in the moon, as well as in the earth, there is a quantity of moisture occupying the sunken hollows of that globe; and although this orb revolves actually in the ether, and outside the centres not merely of the universe, but even of our earth, yet the mass of water in the moon is not at all hindered from cleaving invariably to the orb of the moon, and tending to the centre of the body to which it belongs. So, by this instance of the pheno[82]mena of the moon, the science of optics amends the received theory of mechanics, and confirms on this point my introduction to my Commentaries upon the Motions of the Planet Mars.20 The followers of the Samian philosophy (for I may use this epithet to designate the philosophy originated by the Samians, Pythagoras and Aristarchus) have a strong argument against the apparent immobility of the earth provided in the phenomena of the moon. For we are taught by optics that if any one of us was in the moon, to him the moon, his abode, would seem [83]quite immovable, but our earth and sun and all the rest of the heavenly bodies movable; for the conclusions of sight are thus related. ......Buy Now (To Read More)

Product details

Ebook Number: 46036
Author: Galilei, Galileo
Release Date: Jun 19, 2014
Format: eBook
Language: English

Contributors

Contributor (Author): Kepler, Johannes, 1571-1630


Translator: Carlos, Edward Stafford