Galileo’s Letter to the Vatican in Defense of His Astronomical Work, a Copy Created During the Banishment of his Work

An anonymous copy, almost certainly written at a time when only manuscript copies were being circulated, late 17th century to early 18th century

In 1610, Galileo published his Sidereus Nuncius (Starry Messenger), describing the observations that he had made with his new, much stronger telescope, amongst them, the Galilean moons of Jupiter. With these observations and additional observations that followed, such as the phases of Venus, he promoted the heliocentric theory of Nicolaus Copernicus published in De revolutionibus orbium coelestium in 1543. Galileo’s opinions were met with opposition within the Catholic Church, and in 1616 the Inquisition declared heliocentrism to be “formally heretical”. Galileo went on to propose a theory of tides in 1616, and of comets in 1619; he argued that the tides were evidence for the motion of the Earth.

In 1632, Galileo published his Dialogue Concerning the Two Chief World Systems, which defended heliocentrism, and was immensely popular. Responding to mounting controversy over theology, astronomy and philosophy, the Roman Inquisition tried Galileo in 1633, found him “vehemently suspect of heresy”, and sentenced him to house arrest where he remained until his death in 1642. At that point, heliocentric books were banned and Galileo was ordered to abstain from holding, teaching or defending heliocentric ideas after the trial.

On the publication of Sidereus Nuncius the British Ambassador Sir Henry Wotton sent a letter to King James about the discovery of four ‘new planets’ revolving around Jupiter, enclosing a copy of the book. He added that the new little planets would affect Jupiter’s perceived astrological influence: ‘For the virtue of the new planets must needs vary the Judicial part’. A year later, a query on this matter was put to Galileo by his friend at the Vatican, Piero Dini: if the Stella Medici really existed, how could one ascertain their influence?

Galileo’s affirmation that the new stars do really exist appears here as inseparable from his stating that they must also, like Jupiter, exert an influence. He also proposes what could be the first program for astrological research: from past case-histories, by scrutinizing the configuration of the little Jupiter-moons, one should in principle be able to ascertain how they work. He here disagreed with Kepler. In his letter to Galileo of 1610, the Imperial Mathematician had expressed the view that, because the new moons did not depart appreciably from the side of Jupiter, viewed from Earth, therefore they could not exert any ‘influence’ – and they must exist purely for the benefit of the inhabitants of Jupiter.

Manuscript, late 17th century, early 18th century, 18 cm x 25 cm, consisting of 10 unnumbered leaves, filled in on the front and back. There is an annotation by a different, later hand which refers to a printed edition of Galileo’s works “see work of Galileo, Padua edition volume II page 430”. The Padua edition was published in 1744, so after the creation of this manuscript.

Selections from the text:

“I, for a full two years hitherto, have with my instrument, rather with tens of my instruments, carried out hundreds of thousands of experiments with thousands and thousands of objects, both near and far, both large and small, both bright and dark, I fail to see how it could occur to anyone that I might quite simply carry on being deceived in my observations, and that, between the perspicacity of another’s genius and the stupidity of my own, could fall such wide discrepancy, that they, without ever having seen my instrument, have discovered this fault… Let me add that it is not only my instrument, or the others by me constructed, that make visible the four Jovial planets, but all others too, made in whatever place by whichever craftsmen, provided they are well worked and show other objects large and distinct…

“As for the other objection, namely that if such Planets are indeed real, they must on account of their smallness remain ineffective, I cannot see how this can be held against me, since I have put forth not a word on their effectiveness or their influences; such that if anyone judge them superfluous, redundant and of no use to the world, let them take issue with nature or God, not with me, for I have naought to do with it, claiming no more than to have shown them there in the sky, revolving by their own proper motion round the star of Jove….

“I certainly do not believe that in ancient and ruder centuries nature forebore to produce the immense variety of plants and animals, of gems and metals and other minerals; to make for each one of those animals member, muscle and joint; furthermore, that she failed to move the celestial sphere, and in sum, to produce and work her effects; simply because these inexpert people knew not the virtues of the plants, the stones and the fossils, nor understood the uses of all the parts of the animals, nor discerned the courses of the stars: and indeed for my part what a ridiculous thing would it be to believe that the things of nature come into being only when we come to discover them and to understand them…

“And if others too are eager to press me to say what particular influence I believe depends on these new Planets I have recently discovered; I would respond, that all the influences which they have hitherto attributed to Jupiter alone, are derived no more from Jupiter than from his satellites, and having believed that Jupiter operates alone, and not having known that he had four companions, not one authority has mastered the manner in which Jupiter might cease to have them close by and to co-operate with them. How to distinguish more particularly their effects, I would not know, unless someone were to remove his satellites from his side, and for some time make him work alone. And who would know if anger, love, hatred and other such passions reside in the brain or in the heart, lest first he try living for some time without brain or without heart?

“Now I add further, that if it is true, as these astrologers and many philosophers affirm, that the stars work their operations lumine et motu, by light and motion, and if it is further true that the larger lights influence more effectively, it follows that velocity of motion and swiftness and frequency of conjunction give great advantage over the sluggish tardiness of those that wander slowly: and if this is so, the influence of the four new Planets must be most vigorous, their being endowed with such rapid orbital periods, that the slowest completes its revolution round Jupiter in little less than sixteen days, and the swiftest in less than two days. What they lack therefore, due to dimness of light, may be best compensated for by swiftness of motion; and if the light of all four together is, e.g., the equivalent of half the light of Saturn, they are, on the contrary, thousands and thousands of times swifter than him. So how much they may assist and alter the effects of Jupiter (assuming, indeed, we take him as primary among the five), may from future observations in particular be gathered, and at present be generally estimated by conjecture as to what it implies to have four stars now conjunct, now divided, now all oriental, now all occidental, now some dexter and some sinister, now all or some direct, now by contrast retrograde, now full of light and now obscured and eclipsed; all the which variations alternating from day to day. But should anyone insist on denying influences where the light of the celestial bodies which do influence does not reach, therefore saying that motion without light has no effect, I would first ask him what light have those places in the heavens where there is not a single star, nor any light of their own; as in the case of the ascendant, the midheaven, the part of fortune, and then all those other places which they, the astrologers, move by direction,10 and which, without a single star, are of all the effects that follow, in their opinion, authors. Moreover, the stars beneath our horizon must have no effect, since their light does not reach our hemisphere; or if their potency is strong enough to penetrate the celestial globe, then the so many and so large stars of southern skies ought not to be neglected. Besides, who can say the light of the Medicean Planets does not reach the earth? Would we still make of our eyes the measure of the effusion of all the lights, so that where the image of a luminous object does not make itself sensible to us, there must we declare that its light does not reach? Perhaps eagles and wolves can see such stars, which remain hidden to our feeble vision. Whereas, since visible images are but forms of light, or at least cannot diffuse without light, wherever these images arrive, there must arrive their light: now, if the images of the four Medicean Planets in diffusing fade away and are lost before they can reach earth, all Murano’s lenses put together would not suffice to make them visible, because what is not there cannot be magnified, and dilation and augmentation assume the existence of something which can dilate and augment: therefore, since the images of the four Medicean Planets can be seen so large and luminous through the telescope, it cannot be denied that their light diffuses brightly enough as far as the earth. Finally I might add, if it requires a most apparent and perceptible illumination in order to exert influence, then the effects of Mercury must truly remain null or extremely feeble, since his light remains for most of the time, indeed almost always, invisible; and Mars near the Sun, where his visual magnitude is barely one sixtieth part of that which we see at opposition, such that in size he subsides to the apparent magnitude of stars of the fourth order, must have little or no influence. Let us conclude therefore, if the other stars can influence, the Mediceans too do not cease to perform. Lastly, regarding what these Gentleman add, that of such stars, to their belief, there is no lack, I cannot deny nor affirm anything, but merely say for my part that I have not been able to discover any other than these four around Jupiter, and the two in motionless conjunction with Saturn; and I pray that if others have discovered more, they be not displeased to inform me, as I should be most particularly obliged to them. Yet I do not believe, that these Gentlemen mean stars other than the movable and wandering stars, as are the Medicean stars, since to talk about the countless fixed stars is beside the point: and I have already written, how immense is the number of fixed stars invisible to the naked eye: but since they do not induce us to establish new spheres nor to alter the universal system nor to recognize necessarily that no single orb is the centre with respect to which all the stars revolve,12 they can with less scrupulous examination be passed over. And if, as I also esteem, it is the wandering stars these Gentlemen mean in stating their belief that of such there is no lack, whence at the same time arises their difficulty in conceding these four?”