Location via proxy:   [ UP ]  
[Report a bug]   [Manage cookies]                
Everand Logo

Welcome to Everand!

  • Discover millions of ebooks, audiobooks, and so much more with a free trial

    From $11.99/month after trial. Cancel anytime.

    Delphi Collected Works of Galileo Galilei (Illustrated)
    Delphi Collected Works of Galileo Galilei (Illustrated)
    Delphi Collected Works of Galileo Galilei (Illustrated)
    Ebook1,729 pages25 hours

    Delphi Collected Works of Galileo Galilei (Illustrated)

    By Galileo Galilei

    ()

    Read preview

    About this ebook

    Galileo Galilei, the Italian astronomer, physicist, engineer, philosopher and mathematician, played a major role in the scientific revolution of the seventeenth century. His discoveries with the telescope revolutionised astronomy and paved the way for the acceptance of the Copernican heliocentric system, while his formulation of the law of falling bodies and parabolic trajectories marked the beginning of a fundamental change in the study of motion. This comprehensive eBook presents Galileo’s collected works, with numerous illustrations, rare texts appearing in digital print for the first time, informative introductions and the usual Delphi bonus material. (Version 1)


    * Beautifully illustrated with images relating to Galileo’s life and works
    * New introductions, specially written for this collection, by Professor Kenneth Richard Seddon, OBE (QUILL, The Queen’s University of Belfast)
    * Features Galileo’s major works, with individual contents tables
    * Images of how the books were first published, giving your eReader a taste of the original texts
    * Excellent formatting of the texts
    * Features four biographies - discover Galileo’s intriguing life
    * Scholarly ordering of texts into chronological order and literary genres


    Please visit www.delphiclassics.com to browse through our range of exciting titles


    CONTENTS:


    The Books
    THE STARRY MESSENGER
    LETTER TO THE GRAND DUCHESS CHRISTINA
    DISCOURSE ON FLOATING BODIES
    DIALOGUE CONCERNING THE TWO CHIEF WORLD SYSTEMS
    DISCOURSES AND MATHEMATICAL DEMONSTRATIONS RELATING TO TWO NEW SCIENCES


    The Biographies
    LIFE OF GALILEO by Sir David Brewster
    THE TRIAL OF GALILEO by A. Mézières
    GALILEO by Robert S. Ball
    BRIEF BIOGRAPHY: GALILEO GALILIEI


    Please visit www.delphiclassics.com to browse through our range of exciting titles or to purchase this eBook as a Parts Edition of individual eBooks


    LanguageEnglish
    PublisherDelphi Classics
    Release dateJan 9, 2017
    ISBN9781786560582
    Delphi Collected Works of Galileo Galilei (Illustrated)

    Read more from Galileo Galilei

    Related to Delphi Collected Works of Galileo Galilei (Illustrated)

    Titles in the series (24)

    View More
    View More

    Related ebooks

    Astronomy & Space Sciences For You

    View More
    View More

    Related podcast episodes

    Related articles

    • UNLIMITED

      When the Heavens Stopped Being Perfect

      Mar 29, 2018

      I have in my hand a little book titled The Starry Messenger (Sidereus Nuncius in its original Latin), written by the Italian mathematician and scientist Galileo Galilei in 1610. There were 550 books in the first printing of Messenger. One hundred and

      11 min read

    • UNLIMITED

      Galileo Galilei

      Feb 28, 2020

      Galileo Galilei
      4 min read

    • UNLIMITED

      The great DEBATE

      Apr 22, 2021

      The great DEBATE
      6 min read

    • UNLIMITED

      Galileo Galilei

      Jul 14, 2023

      Galileo Galilei
      3 min read

    • UNLIMITED

      Giovanni Battista Riccioli

      Nov 7, 2019

      Giovanni Battista Riccioli
      2 min read

    • UNLIMITED

      Governing the Planets

      Jul 10, 2019

      Governing the Planets
      9 min read

    • UNLIMITED

      Galileo And The Telescope

      May 3, 2021

      If you were to ever find yourself strolling through the Mueseo Galileo in the city of Florence, Italy, you would likely chance upon a rather ordinary object. At least, that’s what it looks like at first glance. Do give it a second peek, as this relic

      1 min read

    • UNLIMITED

      Nine Rebel Astronomy Theories That Went Dark

      Apr 17, 2024

      The history of astronomy has hinged on radical ideas that transformed our understanding of the cosmos and our place in it. The most obvious of these may be  the discovery in the 16th century that the Earth and other planets orbit the sun. An unpopula

      5 min read

    • UNLIMITED

      Other Astronomers We Should Remember

      Aug 3, 2022

      Astronomy as we know it today had its start in Europe around the start of the 17th century. The Greeks and the Muslims had made discoveries earlier, but they were shackled by a conviction that the Earth was the centre of the cosmos, and by a confusio

      3 min read

    • UNLIMITED

      Top Ten Unsung Geniuses: For these scientists, success and fame did not come in equal measure.

      Oct 16, 2014

      It’s easy to name science and math geniuses. I can just flip open my old book from the 1960s, which lists “100 Great Scientists”; it contains all the names you’d find on most popular lists of scientific geniuses: Einstein, Newton, Maxwell, Gauss, Boh

      5 min read

    • UNLIMITED

      The Joy of Cosmic Mediocrity

      Dec 26, 2019

      One of the greatest debates in the long history of astronomy has been that of exceptionalism versus mediocrity—and one of the great satisfactions of modern times has been watching the arguments for mediocrity emerge triumphant. Far more than just a h

      10 min read

    • UNLIMITED

      If Not Darwin, Who?: An alternative history of the great ideas of science.

      Dec 15, 2016

      What would physics look like if Einstein had never existed, or biology without Darwin? In one view, nothing much would change—the discoveries they made and theories they devised would have materialized anyway sooner or later. That’s the odd thing abo

      13 min read

    • UNLIMITED

      Galileo Galilei

      Aug 11, 2022

      Galileo Galilei
      1 min read

    • UNLIMITED

      Do You Know These Scientific Pioneers?

      Nov 25, 2020

      It’s easy to name science and math geniuses. I can just flip open my old book from the 1960s, which lists “100 Great Scientists”; it contains all the names you’d find on most popular lists of scientific geniuses: Einstein, Newton, Maxwell, Gauss, Boh

      5 min read

    • UNLIMITED

      Father, Son And The Changing Universe

      Jun 9, 2021

      When we think of the people who started modern astronomy, 400 or 500 years ago — liberating it from the erroneous concepts that had held it back for a thousand years or more — some names come quickly to mind. The great Galileo of course, plus Coperni

      2 min read

    • UNLIMITED

      A Storm On The Sun

      Jul 14, 2022

      A Storm On The Sun
      12 min read

    • UNLIMITED

      Visions Of The Universe

      Feb 14, 2020

      Visions Of The Universe
      4 min read

    • UNLIMITED

      Reach For The Stars

      Jun 17, 2020

      Reach For The Stars
      3 min read

    • UNLIMITED

      The First Deep Sky Atlas

      Feb 6, 2022

      The First Deep Sky Atlas
      9 min read

    • UNLIMITED

      Book Reviews

      Oct 19, 2021

      By Amber Gartrell ISBN: 978-1108477550 Cambridge University Press (2021) – $99.99 www.cambridge.org Once upon a time there were two brothers. The Greeks knew them as the Dioskouroi, the Romans as the Dioscuri. Sons of Leda, queen of Sparta, they had

      5 min read

    Related categories

    Reviews for Delphi Collected Works of Galileo Galilei (Illustrated)

    0 ratings

    0 ratings0 reviews

    What did you think?

    Tap to rate

    Review must be at least 10 words

      Book preview

      Delphi Collected Works of Galileo Galilei (Illustrated) - Galileo Galilei

      The Collected Works of

      GALILEO GALILEI

      (1564-1642)

      Contents

      The Books

      THE STARRY MESSENGER

      LETTER TO THE GRAND DUCHESS CHRISTINA

      DISCOURSE ON FLOATING BODIES

      DIALOGUE CONCERNING THE TWO CHIEF WORLD SYSTEMS

      DISCOURSES AND MATHEMATICAL DEMONSTRATIONS RELATING TO TWO NEW SCIENCES

      The Biographies

      LIFE OF GALILEO by Sir David Brewster

      THE TRIAL OF GALILEO by A. Mézières

      GALILEO by Robert S. Ball

      BRIEF BIOGRAPHY: GALILEO GALILIEI

      The Delphi Classics Catalogue

      © Delphi Classics 2017

      Version 1

      The Collected Works of

      GALILEO GALILEI

      By Delphi Classics, 2017

      With new introductions by

      Professor Kenneth Richard Seddon, OBE

      (QUILL, The Queen’s University of Belfast)

      COPYRIGHT

      Collected Works of Galileo Galilei

      First published in the United Kingdom in 2017 by Delphi Classics.

      © Delphi Classics, 2017.

      All rights reserved.  No part of this publication may be reproduced, stored in a retrieval system, or transmitted, in any form or by any means, without the prior permission in writing of the publisher, nor be otherwise circulated in any form other than that in which it is published.

      ISBN: 978 1 78656 058 2

      Delphi Classics

      is an imprint of

      Delphi Publishing Ltd

      Hastings, East Sussex

      United Kingdom

      Contact: sales@delphiclassics.com

      www.delphiclassics.com

      Other classic Science and Philosophy eBooks available

      These comprehensive editions are beautifully illustrated and offer eReaders some of the greatest scientific works ever written.

      Explore Non-Fiction at Delphi Classics

      The Books

      Pisa, Tuscany, central Italy — Galileo’s birthplace

      The birthplace of Galileo

      Drawing of Pisa in the Renaissance, c. 1540

      THE STARRY MESSENGER

      Translated by Edward Stafford Carlos

      The Oxford English Dictionary defines genius (noun) as the "innate intellectual or creative power of an exceptional or exalted type, such as is attributed to those people considered greatest in any area of art, science, etc.; instinctive and extraordinary capacity for imaginative creation, original thought, invention, or discovery".  The modern media, with their love of superlatives, have devalued this term, but its original meaning remains unsullied in academic circles.  There are few genii in our history, but perhaps the first that is universally recognised was Leonardo da Vinci (15th April 1452 – 2nd May 1519): a true genius and polymath – scientist, artist, inventor - with footprints in almost all areas of academic endeavour – including painting, sculpture, architecture, music, literature, science, mathematics, engineering, anatomy, geology, astronomy, botany, writing, history, and even map making.  He was the archetype of Renaissance man.  A century later, another genius was born in Italy - Galileo Galilei (15th February 1564 – 8th January 1642; see Figure 1) - astronomer, physicist, engineer, philosopher and mathematician.  Albert Einstein and Stephen Hawking – two modern genii - credit him with being the progenitor of modern science, and his work had a profound influence on Sir Isaac Newton, laying the basis of his Laws of Motion, and later Einstein’s Theory of Special Relativity.

      Galileo’s first landmark book was published, in Latin, in 1610 (see Figure 2), revolutionising the science of astronomy.  It was entitled Sidereus Nuncius: this is translated variously as Sidereal Messenger (see Figure 3), Starry Messenger, or Sidereal Message (the most accurate translation).  It was the first astronomical book based on observations made with a telescope, and included studies of the moon, and of hundreds of previously unobserved stars.  Galileo built his own telescope for this study, improving on the design available at the time. His observations of the moon (Figure 4) resulted in his deducing the existence of mountains and valleys on the lunar surface.  His observations of the stars, especially the constellations of Orion (Figure 5) and the Pleiades (Figure 6) resulted in the number of observable stars being up to ten times the number previously observed.  He also examined the Milky Way, and his comments, reproduced here, are both elegant and perceptive. I have observed the essence or substance of the MILKY WAY circle. By the aid of a telescope anyone may behold this in a manner which so distinctly appeals to the senses that all the disputes which have tormented philosophers through so many ages are exploded at once by the unquestionable evidence of our eyes, and we are freed from wordy disputes upon this subject, for the GALAXY is nothing else but a mass of innumerable stars planted together in clusters. Upon whatever part of it you direct the telescope straightway a vast crowd of stars presents itself to view; many of them are tolerably large and extremely bright, but the number of small ones is quite beyond determination.

      Another key feature of this landmark volume is the discovery of the moons of Jupiter, which Galileo referred to as Medicean Stars, named for the four Medici brothers.  He wrote: I therefore concluded, and decided unhesitatingly, that there are three stars in the heavens moving about Jupiter, as Venus and Mercury round the Sun; which at length was established as clear as daylight by numerous other subsequent observations. These observations also established that there are not only three, but four, erratic sidereal bodies performing their revolutions round Jupiter, observations of whose changes of position made with more exactness on succeeding nights.  They are now known as Galilean moons, and named Io, Europa, Ganymede, and Callisto (all lovers of Zeus, or Jupiter) by Simon Marius (who independently discovered them a few days after Galileo).

      And so the seeds were sown.  Enlightened scientists, philosophers and artists greeted Sidereus Nuncius with acclaim. But many rejected the findings, ascribing them to lens defects in the telescope, and denied the existence of Jupiter’s moons. Independent verification of Galileo’s observations soon followed, confirming his conclusions that four moons orbited Jupiter.

      Naming the moons after the Medici brothers moved the content of the book from scientific discourse to a political issue.  Moreover, this book challenged the Church’s position – the proof that the Milky Way consisted of a multitude of stars, and not the fiery exhalation of stars (the Aristotelian view), that Earth’s moon was not a perfect sphere, and his belief in the absolute truth of the Copernican heliocentric system (already downgraded to a hypothesis by the Church) were all seen to challenge scripture.

      In the current post-truth (relating to, or denoting, circumstances in which objective facts are less influential in shaping public opinion than appeals to emotion and personal belief) era, we see a parallel for Galileo’s situation.  In contradiction to the compelling weight of scientific evidence, in 1616 or 2016, it is possible to ignore or arbitrarily select data and arguments, and come to whatever conclusion you desire.  Post-truth, then as now, is a weapon of ignorance and superstition, wielded by unscrupulous politicians and religious leaders.  Whether it is a Church unwilling to accept a heliocentric system, creationists, or climate-change deniers, the same forces of ignorance and bigotry pervade public opinion.

      Figure 1:  A painting of Galileo Galilei (1636) by Justus Sustermans (1597–1681), currently displayed in the National Maritime Museum, Greenwich, London.

      Figure 2:  The title page of Sidereus Nuncius, published 13 March, 1610.

      Figure 3:  The title page of' ‘The Sidereal Messenger’, published 1880.

      CONTENTS

      PREFATORY NOTE.

      INTRODUCTION.

      THE ASTRONOMICAL MESSENGER

      A PART OF THE PREFACE TO KEPLER’S DIOPTRICS FORMING A CONTINUATION OF GALILEO’S SIDEREAL MESSENGER.

      ENDNOTES.

      Figure 4:  A composite of Galileo’s sketches of the moon from ‘Sidereus Nuncius’

      Figure 5:  The Belt and Sword of the Orion Constellation.  According to Galileo, The well known or old stars, for the sake of distinction, I have depicted of larger size, and I have outlined them with a double line; the others, invisible to the naked eye, I have marked smaller and with one line only.

      Figure 6:  The Pleiades Constellation. According to Galileo, The well known or old stars, for the sake of distinction, I have depicted of larger size, and I have outlined them with a double line; the others, invisible to the naked eye, I have marked smaller and with one line only.

      PREFATORY NOTE.

      About five years ago I was engaged in preparing a catalogue of the ancient books which belong to Christ’s Hospital. One portion of these books consisted of a collection of ancient mathematical works presented at various times for the use of that part of the school which is known as the Royal Mathematical Foundation of King Charles II. Amongst them were some well known by name to every mathematical student, but which few have ever seen. Perhaps the most interesting of them all was a little volume, printed in London in 1653, containing Gassendi’s Explanation of the Ptolemaic and Copernican Systems of Astronomy, as well as that of Tycho Brahe, Galileo’s Sidereus Nuncius, and Kepler’s Dioptrics. I found Galileo’s account of his astronomical discoveries so interesting, both in matter and in style, that I translated it as a recreation from school-work. I venture to think that others also will be interested in following Galileo through the apprehension of his famous discoveries, and in reading the language in which he announced them.

      INTRODUCTION.

      In 1609, Galileo, then Professor of Mathematics at Padua, in the service of the Venetian Republic, heard from a correspondent at Paris of the invention of a telescope, and set to work to consider how such an instrument could be made. The result was his invention of the telescope known by his name, and identical in principle with the modern opera-glass. In a maritime and warlike State, the advantages to be expected from such an invention were immediately recognised, and Galileo was rewarded with a confirmation of his Professorship for life, and a handsome stipend, in recognition of his invention and construction of the first telescope seen at Venice. In his pamphlet, The Sidereal Messenger, here translated, Galileo relates how he came to learn the value of the telescope for astronomical research; and how his observations were rewarded by numerous discoveries in rapid succession, and at[viii] length by that of Jupiter’s satellites. Galileo at once saw the value of this discovery as bearing upon the establishment of the Copernican system of astronomy, which had met with slight acceptance, and indeed as yet had hardly any recommendation except that of greater simplicity. Kepler had just published at Prague his work on the planet Mars (Commentaria de motibus Stellæ Martis), on which he had been engaged apparently for eight years; there he heard of Galileo’s discoveries, and at length was invited by Galileo himself, through a common friend, Giuliano de’ Medici, ambassador of the Grand-Duke of Tuscany, Cosmo de’ Medici II., to the Emperor Rudolph II., to correspond with Galileo on the subject of these discoveries. The Emperor also requested his opinion, and Kepler accordingly examined Galileo’s Sidereal Messenger in a pamphlet, entitled A Discussion with the Sidereal Messenger (Florence, 1610).

      In this Discussion Kepler gives reasons for accepting Galileo’s observations — although he was not able to verify them from want of a telescope — and entirely supports Galileo’s views and conclusions, adducing his own previous speculations, or pointing out, as in the case of Galileo’s idea of earth-light on the moon, the previous conception of the same explanation of the phenomenon. He rejects, however, Galileo’s explanation of the copper colour of the moon in eclipses. Kepler ends by expressing unbounded enthusiasm at the discovery of Jupiter’s satellites, and the argument it furnishes in support of the Copernican theory.

      Soon after, in 1611, Kepler published another pamphlet, his Narrative, giving an account of actual observations made in verification of Galileo’s discoveries by himself and several friends, whose names he gives, with a telescope made by Galileo, and belonging to Ernest, Elector and Archbishop of Cologne. Kepler and his friends saw the lunar mountains and three of the satellites of Jupiter, but failed to make out any signs of the ring of Saturn corresponding to the imperfect description of Galileo.

      Kepler had previously published a treatise on Optics (Frankfort, 1604). He now extended it to the consideration of the theory of the telescope, and explained the principle of Galileo’s telescope; he also showed another combination of lenses which would produce a similar effect. This was the principle of the common astronomical telescope, often called, from this circumstance, Kepler’s telescope, though he did not construct it. The account of Galileo’s later astronomical discoveries of Saturn’s ring and the phases of Venus is taken from the preface of this work. — (Kepler’s Dioptrics; Augsburg, 1611.)

      In 1612 Galileo published a series of observations of solar spots, and in 1618 some observations of three comets. There exist also long series of minute observations of Jupiter and his satellites, continued to November 1619. — (Galileo’s Works; Florence, 1845.)

      Further astronomical researches may have been hindered by failing sight. One more astronomical discovery, however, that of the moon’s librations, was made as late as 1637, and the announcement of it is dated dalla mia carcere di Arcetri. Galileo died January 8, 1642.

      The following editions have been used for the translation: —

      Galileo’s Works.

      1. Florence, 1718.

      2. Padua, 1744.

      3. Florence, 1842-56.

      Sidereus Nuncius.

      1. Venice, 1610.

      2. London, 1653.

      Kepler’s Works, ed. C. Frisch. Frankfurt a. M., 1858-71.

      Prodromus dissertationum mathematicarum continens Mysterium Cosmographicum de admirabili proportione orbium cœlestium. Tübingen, 1596.

      Astronomia nova αἰτιολογητός (Commentaria de motibus stellæ Martis). [Prague,] 1609.

      THE

      SIDEREAL MESSENGER

      UNFOLDING GREAT AND MARVELLOUS SIGHTS,

      AND PROPOSING THEM TO THE ATTENTION OF EVERY ONE,

      BUT ESPECIALLY PHILOSOPHERS AND ASTRONOMERS,

      BEING SUCH AS HAVE BEEN OBSERVED BY

      GALILEO GALILEI

      A GENTLEMAN OF FLORENCE,

      PROFESSOR OF MATHEMATICS IN THE UNIVERSITY OF PADUA,

      WITH THE AID OF A

      TELESCOPE

      lately invented by him,

      Respecting the Moon’s Surface, an innumerable number of Fixed Stars,

      the Milky Way, and Nebulous Stars, but especially respecting

      Four Planets which revolve round the Planet Jupiter at

      different distances and in different periodic times, with

      amazing velocity, and which, after remaining

      unknown to every one up to this day, the

      Author recently discovered, and

      determined to name the

      MEDICEAN STARS.

      Venice 1610.

      TO THE MOST SERENE

      COSMO DE’ MEDICI, THE SECOND,

      FOURTH GRAND-DUKE OF TUSCANY.

      THERE is certainly something very noble and large-minded in the intention of those who have endeavoured to protect from envy the noble achievements of distinguished men, and to rescue their names, worthy of immortality, from oblivion and decay. This desire has given us the lineaments of famous men, sculptured in marble, or fashioned in bronze, as a memorial of them to future ages; to the same feeling we owe the erection of statues, both ordinary and equestrian; hence, as the poet¹ says, has originated expenditure, mounting to the stars, upon columns and pyramids; with this desire, lastly, cities have been built, and distinguished by the names of those men, whom the gratitude of posterity thought worthy of being handed down to all ages. For the state of the human mind is such, that unless it be continually stirred by the counterparts² of matters, obtruding themselves upon it from without, all recollection of the matters easily passes away from it.

      But others, having regard for more stable and more lasting monuments, secured the eternity of the fame of great men by placing it under the protection, not of marble or bronze, but of the Muses’ guardianship and the imperishable monuments of literature. But why do I mention these things, as if human wit, content with these regions, did not dare to advance further; whereas, since she well understood that all human monuments do perish at last by violence, by weather, or by age, she took a wider view, and invented more imperishable signs, over which destroying Time and envious Age could claim no rights; so, betaking herself to the sky, she inscribed on the well-known orbs of the brightest stars — those everlasting orbs — the names of those who, for eminent and god-like deeds, were accounted worthy to enjoy an eternity in company with the stars. Wherefore the fame of Jupiter, Mars, Mercury, Hercules, and the rest of the heroes by whose names the stars are called, will not fade until the extinction of the splendour of the constellations themselves.

      But this invention of human shrewdness, so particularly noble and admirable, has gone out of date ages ago, inasmuch as primeval heroes are in possession of those bright abodes, and keep them by a sort of right; into whose company the affection of Augustus in vain attempted to introduce Julius Cæsar; for when he wished that the name of the Julian constellation should be given to a star, which appeared in his time, one of those which the Greeks and the Latins alike name, from their hair-like tails, comets, it vanished in a short time and mocked his too eager hope. But we are able to read the heavens for your highness, most Serene Prince, far more truly and more happily, for scarcely have the immortal graces of your mind begun to shine on earth, when bright stars present themselves in the heavens, like tongues to tell and celebrate your most surpassing virtues to all time. Behold therefore, four stars reserved for your famous name, and those not belonging to the common and less conspicuous multitude of fixed stars, but in the bright ranks of the planets — four stars which, moving differently from each other, round the planet Jupiter, the most glorious of all the planets, as if they were his own children, accomplish the courses of their orbits with marvellous velocity, while all the while with one accord they complete all together mighty revolutions every ten years round the centre of the universe, that is, round the Sun.

      But the Maker of the Stars himself seemed to direct me by clear reasons to assign these new planets to the famous name of your highness in preference to all others. For just as these stars, like children worthy of their sire, never leave the side of Jupiter by any appreciable distance, so who does not know that clemency, kindness of heart, gentleness of manners, splendour of royal blood, nobleness in public functions, wide extent of influence and power over others, all of which have fixed their common abode and seat in your highness, — who, I say, does not know that all these qualities, according to the providence of God, from whom all good things do come, emanate from the benign star of Jupiter? Jupiter, Jupiter, I maintain, at the instant of the birth of your highness having at length emerged from the turbid mists of the horizon, and being in possession of the middle quarter of the heavens, and illuminating the eastern angle, from his own royal house, from that exalted throne, looked out upon your most happy birth, and poured forth into a most pure atmosphere all the brightness of his majesty, in order that your tender body and your mind — though that was already adorned by God with still more splendid graces — might imbibe with your first breath the whole of that influence and power. But why should I use only plausible arguments when I can almost absolutely demonstrate my conclusion? It was the will of Almighty God that I should be judged by your most serene parents not unworthy to be employed in teaching your highness mathematics, which duty I discharged, during the four years just passed, at that time of the year when it is customary to take a relaxation from severer studies. Wherefore, since it evidently fell to my lot by God’s will, to serve your highness, and so to receive the rays of your surpassing clemency and beneficence in a position near your person, what wonder is it if you have so warmed my heart that it thinks about scarcely anything else day and night, but how I, who am indeed your subject not only by inclination, but also by my very birth and lineage, may be known to be most anxious for your glory, and most grateful to you? And so, inasmuch as under your patronage, most serene Cosmo, I have discovered these stars, which were unknown to all astronomers before me, I have, with very good right, determined to designate them with the most august name of your family. And as I was the first to investigate them, who can rightly blame me if I give them a name, and call them the Medicean Stars, hoping that as much consideration may accrue to these stars from this title, as other stars have brought to other heroes? For not to speak of your most serene ancestors, to whose everlasting glory the monuments of all history bear witness, your virtue alone, most mighty sire, can confer on those stars an immortal name; for who can doubt that you will not only maintain and preserve the expectations, high though they be, about yourself, which you have aroused by the very happy beginning of your government, but that you will also far surpass them, so that when you have conquered others like yourself, you may still vie with yourself, and become day by day greater than yourself and your greatness?

      Accept, then, most clement Prince, this addition to the glory of your family, reserved by the stars for you; and may you enjoy for many years those good blessings, which are sent to you not so much from the stars as from God, the Maker and Governor of the stars.

      Your Highness’s most devoted servant,

      Galileo Galilei.

      Padua, March 12, 1610.

      THE ASTRONOMICAL MESSENGER

      Containing and setting forth Observations lately made with the

      aid of a newly invented Telescope respecting the Moon’s

      Surface, the Milky Way, Nebulous Stars, an

      innumerable multitude of Fixed Stars, and

      also respecting Four Planets never before

      seen, which have been named

      THE COSMIAN STARS.³

      Introduction.

      IN the present small treatise I set forth some matters of great interest for all observers of natural phenomena to look at and consider. They are of great interest, I think, first, from their intrinsic excellence; secondly, from their absolute novelty; and lastly, also on account of the instrument by the aid of which they have been presented to my apprehension.

      The number of the Fixed Stars which observers have been able to see without artificial powers of sight up to this day can be counted. It is therefore decidedly a great feat to add to their number, and to set distinctly before the eyes other stars in myriads, which have never been seen before, and which surpass the old, previously known, stars in number more than ten times.

      Again, it is a most beautiful and delightful sight to behold the body of the Moon, which is distant from us nearly sixty semi-diameters⁴ of the Earth, as near as if it was at a distance of only two of the same measures; so that the diameter of this same Moon appears about thirty times larger, its surface about nine hundred times, and its solid mass nearly 27,000 times larger than when it is viewed only with the naked eye; and consequently any one may know with the certainty that is due to the use of our senses, that the Moon certainly does not possess a smooth and polished surface, but one rough and uneven, and, just like the face of the Earth itself, is everywhere full of vast protuberances, deep chasms, and sinuosities.

      Then to have got rid of disputes about the Galaxy or Milky Way, and to have made its nature clear to the very senses, not to say to the understanding, seems by no means a matter which ought to be considered of slight importance. In addition to this, to point out, as with one’s finger, the nature of those stars which every one of the astronomers up to this time has called nebulous, and to demonstrate that it is very different from what has hitherto been believed, will be pleasant, and very fine. But that which will excite the greatest astonishment by far, and which indeed especially moved me to call the attention of all astronomers and philosophers, is this, namely, that I have discovered four planets, neither known nor observed by any one of the astronomers before my time, which have their orbits round a certain bright star, one of those previously known, like Venus and Mercury round the Sun, and are sometimes in front of it, sometimes behind it, though they never depart from it beyond certain limits. All which facts were discovered and observed a few days ago by the help of a telescope⁵ devised by me, through God’s grace first enlightening my mind.

      Perchance other discoveries still more excellent will be made from time to time by me or by other observers, with the assistance of a similar instrument, so I will first briefly record its shape and preparation, as well as the occasion of its being devised, and then I will give an account of the observations made by me.

      Galileo’s account of the invention of his telescope.

      About ten months ago a report reached my ears that a Dutchman had constructed a telescope, by the aid of which visible objects, although at a great distance from the eye of the observer, were seen distinctly as if near; and some proofs of its most wonderful performances were reported, which some gave credence to, but others contradicted. A few days after, I received confirmation of the report in a letter written from Paris by a noble Frenchman, Jaques Badovere, which finally determined me to give myself up first to inquire into the principle of the telescope, and then to consider the means by which I might compass the invention of a similar instrument, which a little while after I succeeded in doing, through deep study of the theory of Refraction; and I prepared a tube, at first of lead, in the ends of which I fitted two glass lenses, both plane on one side, but on the other side one spherically convex, and the other concave. Then bringing my eye to the concave lens I saw objects satisfactorily large and near, for they appeared one-third of the distance off and nine times larger than when they are seen with the natural eye alone. I shortly afterwards constructed another telescope with more nicety, which magnified objects more than sixty times. At length, by sparing neither labour nor expense, I succeeded in constructing for myself an instrument so superior that objects seen through it appear magnified nearly a thousand times, and more than thirty times nearer than if viewed by the natural powers of sight alone.

      Galileo’s first observations with his telescope.

      It would be altogether a waste of time to enumerate the number and importance of the benefits which this instrument may be expected to confer, when used by land or sea. But without paying attention to its use for terrestrial objects, I betook myself to observations of the heavenly bodies; and first of all, I viewed the Moon as near as if it was scarcely two semi-diameters⁶ of the Earth distant. After the Moon, I frequently observed other heavenly bodies, both fixed stars and planets, with incredible delight; and, when I saw their very great number, I began to consider about a method by which I might be able to measure their distances apart, and at length I found one. And here it is fitting that all who intend to turn their attention to observations of this kind should receive certain cautions. For, in the first place, it is absolutely necessary for them to prepare a most perfect telescope, one which will show very bright objects distinct and free from any mistiness, and will magnify them at least 400 times, for then it will show them as if only one-twentieth of their distance off. For unless the instrument be of such power, it will be in vain to attempt to view all the things which have been seen by me in the heavens, or which will be enumerated hereafter.

      But in order that any one may be a little more certain about the magnifying power of his instrument, he shall fashion two circles, or two square pieces of paper, one of which is 400 times greater than the other, but that will be when the diameter of the greater is twenty times the length of the diameter of the other. Then he shall view from a distance simultaneously both surfaces, fixed on the same wall, the smaller with one eye applied to the telescope, and the larger with the other eye unassisted; for that may be done without inconvenience at one and the same instant with both eyes open. Then both figures will appear of the same size, if the instrument magnifies objects in the desired proportion.

      After such an instrument has been prepared, the Method of measuring small angular distances between heavenly bodies by the size of the aperture of the telescope.method of measuring distances remains for inquiry, and this we shall accomplish by the following contrivance: —

      For the sake of being more easily understood, I will suppose a tube A B C D.⁷ Let E be the eye of the observer; then, when there are no lenses in the tube rays from the eye to the object F G would be drawn in the straight lines E C F, E D G, but when the lenses have been inserted, let the rays go in the bent lines E C H, E D I, — for they are contracted, and those which originally, when unaffected by the lenses, were directed to the object F G, will include only the part H I. Hence the ratio of the distance E H to the line H I being known, we shall be able to find, by means of a table of sines, the magnitude of the angle subtended at the eye by the object H I, which we shall find to contain only some minutes. But if we fit on the lens C D thin plates of metal, pierced, some with larger, others with smaller apertures, by putting on over the lens sometimes one plate, sometimes another, as may be necessary, we shall construct at our pleasure different subtending angles of more or fewer minutes, by the help of which we shall be able to measure conveniently the intervals between stars separated by an angular distance of some minutes, within an error of one or two minutes. But let it suffice for the present to have thus slightly touched, and as it were just put our lips to these matters, for on some other opportunity I will publish the theory of this instrument in completeness.

      Now let me review the observations made by me during the two months just past, again inviting the attention of all who are eager for true philosophy to the beginnings which led to the sight of most important phenomena.

      The Moon. Ruggedness of its surface. Existence of lunar mountains and valleys. Let me speak first of the surface of the Moon, which is turned towards us. For the sake of being understood more easily, I distinguish two parts in it, which I call respectively the brighter and the darker. The brighter part seems to surround and pervade the whole hemisphere; but the darker part, like a sort of cloud, discolours the Moon’s surface and makes it appear covered with spots. Now these spots, as they are somewhat dark and of considerable size, are plain to every one, and every age has seen them, wherefore I shall call them great or ancient spots, to distinguish them from other spots, smaller in size, but so thickly scattered that they sprinkle the whole surface of the Moon, but especially the brighter portion of it. These spots have never been observed by any one before me; and from my observations of them, often repeated, I have been led to that opinion which I have expressed, namely, that I feel sure that the surface of the Moon is not perfectly smooth, free from inequalities and exactly spherical, as a large school of philosophers considers with regard to the Moon and the other heavenly bodies, but that, on the contrary, it is full of inequalities, uneven, full of hollows and protuberances, just like the surface of the Earth itself, which is varied everywhere by lofty mountains and deep valleys.

      Sketches by Galileo to shew: —

      the indentation of the terminator and illuminated summits of mountains in the dark part of the moon;

      the shape of a lunar mountain and of a walled plain.

      Galileo:’Sidereus Nuncius,’ Venice 1610.

      The appearances from which we may gather these conclusions are of the following nature: — On the fourth or fifth day after new-moon, when the Moon presents itself to us with bright horns, the boundary which divides the part in shadow from the enlightened part does not extend continuously in an ellipse, as would happen in the case of a perfectly spherical body, but it is marked out by an irregular, uneven, and very wavy line, as represented in the figure given, for several bright excrescences, as they may be called, extend beyond the boundary of light and shadow into the dark part, and on the other hand pieces of shadow encroach upon the light: — nay, even a great quantity of small blackish spots, altogether separated from the dark part, sprinkle everywhere almost the whole space which is at the time flooded with the Sun’s light, with the exception of that part alone which is occupied by the great and ancient spots. I have noticed that the small spots just mentioned have this common characteristic always and in every case, that they have the dark part towards the Sun’s position, and on the side away from the Sun they have brighter boundaries, as if they were crowned with shining summits. Now we have an appearance quite similar on the Earth about sunrise, when we behold the valleys, not yet flooded with light, but the mountains surrounding them on the side opposite to the Sun already ablaze with the splendour of his beams; and just as the shadows in the hollows of the Earth diminish in size as the Sun rises higher, so also these spots on the Moon lose their blackness as the illuminated part grows larger and larger. Again, not only are the boundaries of light and shadow in the Moon seen to be uneven and sinuous, but — and this produces still greater astonishment — there appear very many bright points within the darkened portion of the Moon, altogether divided and broken off from the illuminated tract, and separated from it by no inconsiderable interval, which, after a little while, gradually increase in size and brightness, and after an hour or two become joined on to the rest of the bright portion, now become somewhat larger; but in the meantime others, one here and another there, shooting up as if growing, are lighted up within the shaded portion, increase in size, and at last are linked on to the same luminous surface, now still more extended. An example of this is given in the same figure. Now, is it not the case on the Earth before sunrise, that while the level plain is still in shadow, the peaks of the most lofty mountains are illuminated by the Sun’s rays? After a little while does not the light spread further, while the middle and larger parts of those mountains are becoming illuminated; and at length, when the Sun has risen, do not the illuminated parts of the plains and hills join together? The grandeur, however, of such prominences and depressions in the Moon seems to surpass both in magnitude and extent the ruggedness of the Earth’s surface, as I shall hereafter show. And here I cannot refrain from mentioning what a remarkable spectacle I observed while the Moon was rapidly approaching her first quarter, a representation of which is given in the same illustration, placed opposite page 16. A protuberance of the shadow, of great size, indented the illuminated part in the neighbourhood of the lower cusp; and when I had observed this indentation longer, and had seen that it was dark throughout, at length, after about two hours, a bright peak began to arise a little below the middle of the depression; this by degrees increased, and presented a triangular shape, but was as yet quite detached and separated from the illuminated surface. Soon around it three other small points began to shine, until, when the Moon was just about to set, that triangular figure, having now extended and widened, began to be connected with the rest of the illuminated part, and, still girt with the three bright peaks already mentioned, suddenly burst into the indentation of shadow like a vast promontory of light.

      At the ends of the upper and lower cusps also certain bright points, quite away from the rest of the bright part, began to rise out of the shadow, as is seen depicted in the same illustration.

      In both horns also, but especially in the lower one, there was a great quantity of dark spots, of which those which are nearer the boundary of light and shadow appear larger and darker, but those which are more remote less dark and more indistinct. In all cases, however, just as I have mentioned before, the dark portion of the spot faces the position of the Sun’s illumination, and a brighter edge surrounds the darkened spot on the side away from the Sun, and towards the region of the Moon in shadow. This part of the surface of the Moon, where it is marked with spots like a peacock’s tail with its azure eyes, is rendered like those glass vases which, through being plunged while still hot from the kiln into cold water, acquire a crackled and wavy surface, from which circumstance they are commonly called frosted glasses.⁸ The lunar spots are suggested to be possibly seas bordered by ranges of mountains.

      Now the great spots of the Moon observed at the same time are not seen to be at all similarly broken, or full of depressions and prominences, but rather to be even and uniform; for only here and there some spaces, rather brighter than the rest, crop up; so that if any one wishes to revive the old opinion of the Pythagoreans, that the Moon is another Earth, so to say, the brighter portion may very fitly represent the surface of the land, and the darker the expanse of water. Indeed, I have never doubted that if the sphere of the Earth were seen from a distance, when flooded with the Sun’s rays, that part of the surface which is land would present itself to view as brighter, and that which is water as darker in comparison. Moreover, the great spots in the Moon are seen to be more depressed than the brighter tracts; for in the Moon, both when crescent and when waning, on the boundary between the light and shadow, which projects in some places round the great spots, the adjacent regions are always brighter, as I have noticed in drawing my illustrations, and the edges of the spots referred to are not only more depressed than the brighter parts, but are more even, and are not broken by ridges or ruggednesses. But the brighter part stands out most near the spots, so that both before the first quarter and about the third quarter also, around a certain spot in the upper part of the figure, that is, occupying the northern region of the Moon, some vast prominences on the upper and lower sides of it rise to an enormous elevation, as the illustrations show. This same spot before the third quarter is seen to be walled round with boundaries of a deeper shade, which just like very lofty mountain summits appear darker on the side away from the Sun, and brighter on the side where they face the Sun; but in the case of the cavities the opposite happens, for the part of them away from the Sun appears brilliant, and that part which lies nearer to the Sun dark and in shadow. After a time, when the enlightened portion of the Moon’s surface has diminished in size, as soon as the whole or nearly so of the spot already mentioned is covered with shadow, the brighter ridges of the mountains mount high above the shade. These two appearances are shown in the illustrations which are given.

      Description of a lunar crater, perhaps Tycho.⁹ There is one other point which I must on no account forget, which I have noticed and rather wondered at. It is this: — The middle of the Moon, as it seems, is occupied by a certain cavity larger than all the rest, and in shape perfectly round. I have looked at this depression near both the first and third quarters, and I have represented it as well as I can in the second illustration already given. It produces the same appearance as to effects of light and shade as a tract like Bohemia would produce on the Earth, if it were shut in on all sides by very lofty mountains arranged on the circumference of a perfect circle; for the tract in the Moon is walled in with peaks of such enormous height that the furthest side adjacent to the dark portion of the Moon is seen bathed in sunlight before the boundary between light and shade reaches half-way across the circular space. But according to the characteristic property of the rest of the spots, the shaded portion of this too faces the Sun, and the bright part is towards the dark side of the Moon, which for the third time I advise to be carefully noticed as a most solid proof of the ruggednesses and unevennesses spread over the whole of the bright region of the Moon. Of these spots, moreover, the darkest are always those which are near to the boundary-line between the light and the shadow, but those further off appear both smaller in size and less decidedly dark; so that at length, when the Moon at opposition becomes full, the darkness of the cavities differs from the brightness of the prominences with a subdued and very slight difference.

      Reasons for believing that there is a difference of constitution in various parts of the Moon’s surface.

      These phenomena which we have reviewed are observed in the bright tracts of the Moon. In the great spots we do not see such differences of depressions and prominences as we are compelled to recognise in the brighter parts, owing to the change of their shapes under different degrees of illumination by the Sun’s rays according to the manifold variety of the Sun’s position with regard to the Moon. Still, in the great spots there do exist some spaces rather less dark than the rest, as I have noted in the illustrations, but these spaces always have the same appearance, and the depth of their shadow is neither intensified nor diminished; they do appear indeed sometimes a little more shaded, sometimes a little less, but the change of colour is very slight, according as the Sun’s rays fall upon them more or less obliquely; and besides, they are joined to the adjacent parts of the spots with a very gradual connection, so that their boundaries mingle and melt into the surrounding region. But it is quite different with the spots which occupy the brighter parts of the Moon’s surface, for, just as if they were precipitous crags with numerous rugged and jagged peaks, they have well-defined boundaries through the sharp contrast of light and shade. Moreover, inside those great spots certain other tracts are seen brighter than the surrounding region, and some of them very bright indeed, but the appearance of these, as well as of the darker parts, is always the same; there is no change of shape or brightness or depth of shadow, so that it becomes a matter of certainty and beyond doubt that their appearance is owing to real dissimilarity of parts, and not to unevennesses only in their configuration, changing in different ways the shadows of the same parts according to the variations of their illumination by the Sun, which really happens in the case of the other smaller spots occupying the brighter portion of the Moon, for day by day they change, increase, decrease, or disappear, inasmuch as they derive their origin only from the shadows of prominences.

      Explanation of the evenness of the illuminated part of the circumference of the Moon’s orb by the analogy of terrestrial phenomena, or by a possible lunar atmosphere. But here I feel that some people may be troubled with grave doubt, and perhaps seized with a difficulty so serious as to compel them to feel uncertain about the conclusion just explained and supported by so many phenomena. For if that part of the Moon’s surface which reflects the Sun’s rays most brightly is full of sinuosities, protuberances, and cavities innumerable, why, when the Moon is increasing, does the outer edge which looks toward the west, when the Moon is waning, the other half-circumference towards the east, and at full-moon the whole circle, appear not uneven, rugged, and irregular, but perfectly round and circular, as sharply defined as if marked out with a pair of compasses, and without the indentations of any protuberances or cavities? And most remarkably so, because the whole unbroken edge belongs to that part of the Moon’s surface which possesses the property of appearing brighter than the rest, which I have said to be throughout full of protuberances and cavities. For not one of the Great Spots extends quite to the circumference, but all of them are seen to be together away from the edge. Of this phenomenon, which affords a handle for such serious doubt, I produce two causes, and so two solutions of the difficulty.

      The first solution which I offer is this: — If the protuberances and cavities in the body of the Moon existed only on the edge of the circle that bounds the hemisphere which we see, then the Moon might, or rather must, show itself to us with the appearance of a toothed wheel, being bounded with an irregular and uneven circumference; but if, instead of a single set of prominences arranged along the actual circumference only, very many ranges of mountains with their cavities and ruggednesses are set one behind the other along the extreme edge of the Moon, and that too not only in the hemisphere which we see, but also in that which is turned away from us, but still near the boundary of the hemisphere, then the eye, viewing them afar off, will not at all be able to detect the differences of prominences and cavities, for the intervals between the mountains situated in the same circle, or in the same chain, are hidden by the jutting forward of other prominences situated in other ranges, and especially if the eye of the observer is placed in the same line with the tops of the prominences mentioned. So on the Earth, the summits of a number of mountains close together appear situated in one plane, if the spectator is a long way off and standing at the same elevation. So when the sea is rough, the tops of the waves seem to form one plane, although between the billows there is many a gulf and chasm, so deep that not only the hulls, but even the bulwarks, masts, and sails of stately ships are hidden amongst them. Therefore, as within the Moon, as well as round her circumference, there is a manifold arrangement of prominences and cavities, and the eye, regarding them from a great distance, is placed in nearly the same plane with their summits, no one need think it strange that they present themselves to the visual ray which just grazes them as an unbroken line quite free from unevennesses. To this explanation may be added another, namely, that there is round the body of the Moon, just as round the Earth, an envelope of some substance denser than the rest of the ether, which is sufficient to receive and reflect the Sun’s rays, although it does not possess so much opaqueness as to be able to prevent our seeing through it — especially when it is not illuminated. That envelope, when illuminated by the Sun’s rays, renders the body of the Moon apparently larger than it really is, and would be able to stop our sight from penetrating to the solid body of the Moon, if its thickness were greater; now, it is of greater thickness about the circumference of the Moon, greater, I mean, not in actual thickness, but with reference to our sight-rays, which cut it obliquely; and so it may stop our vision, especially when it is in a state of brightness, and may conceal the true circumference of the Moon on the side towards the Sun.

      This may be understood more clearly from the adjoining figure, in which the body of the Moon, A B C, is surrounded by an enveloping atmosphere, D E G. An eye at F penetrates to the middle parts of the Moon, as at A, through a thickness, D A, of the atmosphere; but towards the extreme parts a mass of atmosphere of greater depth, E B, shuts out its boundary from our sight. An argument in favour of this is, that the illuminated portion of the Moon appears of larger circumference than the rest of the orb which is in shadow.

      Perhaps also some will think that this same cause affords a very reasonable explanation why the greater spots on the Moon are not seen to reach to the edge of the circumference on any side, although it might be expected that some would be found about the edge as well as elsewhere; and it seems credible that there are spots there, but that they cannot be seen because they are hidden by a mass of atmosphere too thick and too bright for the sight to penetrate.

      Calculation to show that the height of some lunar mountains exceeds four Italian milesdiameter. Suppose the distance to be exactly 1/20th part of the diameter, and let the diagram represent the Moon’s orb, of which C A F is a great circle, E its centre, and C F a diameter, which consequently bears to the diameter of the Earth the ratio 2:7; and since the diameter of the Earth, according to the most exact observations, contains 7000 Italian miles, C F will be 2000, and C E 1000, and the 1/20th part of the whole, C F, 100 miles. Also let C F be a diameter of the great circle which divides the bright part of the Moon from the dark part (for, owing to the very great distance of the Sun from the Moon this circle does not differ sensibly from a great one), and let the distance of A from the point C be 1/20th part of that diameter; let the radius E A be drawn, and let it be produced to cut the tangent line G C D, which represents the ray that illumines the summit, in the point D. Then the arc C A or the straight line C D will be 100 of such units, as C E contains 1000. The sum of the squares of D C, C E is therefore 1,010,000, and the square of D E is equal to this; therefore the whole E D will be more than 1004; and A D will be more than 4 of such units, as C E contained 1000. Therefore the height of A D in the Moon, which represents a summit reaching up to the Sun’s ray, G C D, and separated from the extremity C by the distance C D, is more than 4 Italian miles; but in the Earth there are no mountains which reach to the perpendicular height even of one mile. We are therefore left to conclude that it is clear that the prominences of the Moon are loftier than those of the Earth.

      The faint illumination of the Moon’s disc about new-moon explained to be due to earth-light.

      I wish in this place to assign the cause of another lunar phenomenon well worthy of notice, and although this phenomenon was observed by me not lately, but many years ago, and has been pointed out to some of my intimate friends and pupils, explained, and assigned to its true cause, yet as the observation of it is rendered easier and more vivid by the help of a telescope, I have considered that it would not be unsuitably introduced in this place, but I wish to introduce it chiefly in order that the connection and resemblance between the Moon and the Earth may appear more plainly.

      When the Moon, both before and after conjunction, is found not far from the Sun, not only does its orb show itself to our sight on the side where it is furnished with shining horns, but a slight and faint circumference is also seen to mark out the circle of the dark part, that part, namely, which is turned away from the Sun, and to separate it from the darker background of the sky. But if we examine the matter more closely, we shall see that not only is the extreme edge of the part in shadow shining with a faint brightness, but that the entire face of the Moon, that side, that is, which does not feel the Sun’s glare, is illuminated with a pale light of considerable brightness. At the first glance only a fine circumference appears shining, on account of the darker part of the sky adjacent to it; whereas, on the contrary, the rest of the surface appears dark, on account of the contiguity of the shining horns, which destroys the clearness of our sight. But if any one chooses such a position for himself, that by the interposition of a roof, or a chimney, or some other object between his sight and the Moon, but at a considerable distance from his eye, the shining horns are hidden, and the rest of the Moon’s orb is left exposed to his view, then he will find that this tract of the Moon also, although deprived of sunlight, gleams with considerable light, and particularly so if the gloom of the night has already deepened through the absence of the Sun; for with a darker background the same light appears brighter. Moreover, it is found that this secondary brightness of the Moon, as I may call it, is greater in proportion as the Moon is less distant from the Sun; for it abates more and more in proportion to the Moon’s distance from that body, so much so that after the first quarter, and before the end of the second, it is found to be weak and very faint, although it be observed in a darker sky; whereas, at an angular distance of 60° or less, even during twilight, it is wonderfully bright, so bright indeed that, with the help of a good telescope, the great spots may be distinguished in it.

      This strange brightness has afforded no small perplexity to philosophical minds; and some have published one thing, some another, as the cause to be alleged for it. Some have said that it is the inherent and natural brightness of the Moon; some that it is imparted to that body by the planet Venus; or, as others maintain, by all the stars; while some have said that it comes from the Sun, whose rays, they say, find a way through the solid mass of the Moon. But statements of this kind are disproved without much difficulty, and convincingly demonstrated to be false. For if this kind of light were the Moon’s own, or were contributed by the stars, the Moon would retain it, particularly in eclipses, and would show it then, when left in an unusually dark sky, but this is contrary to experience. For the brightness which is seen on the Moon in eclipses is far less intense, being somewhat reddish, and almost copper-coloured, whereas this is brighter and whiter; besides, the brightness seen during an eclipse is changeable and shifting, for it wanders over the face of the Moon, so that that part which is near the circumference of the circle of shadow thrown by the Earth is bright, but the rest of the Moon is always seen to be dark. From which circumstance we understand without hesitation that this brightness is due to the proximity of the Sun’s rays coming into contact with some denser region which surrounds the Moon as an envelope; owing to which contact a sort of dawn-light is diffused over the neighbouring regions of the Moon, just as the twilight spreads in the morning and evening on the Earth:¹¹ but I will treat more fully of this matter in my book upon the System of the Universe.¹²

      Again, to assert that this sort of light is imparted to the Moon by the planet Venus is so childish as to be undeserving of an answer; for who is so ignorant as not to understand that at conjunction and within an angular distance of 60° it is quite impossible for the part of the Moon turned away from the Sun to be seen by the planet Venus?

      But that this light is derived from the Sun penetrating with its light the solid mass of the Moon, and rendering it luminous, is equally untenable. For then this

      Enjoying the preview?
      Page 1 of 1