"… by sparing neither labour nor expense, 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."
The quotation is from Sidereus Nuncius, the Messenger from the Stars, published in Venice in March 1610. It was Galileo's first scientific publication, and it threw his telescopic discoveries like a bomb into the arena of the learned world. It not only contained news of heavenly bodies "which no mortal had seen before"; it was also written in a new, tersely factual style which no scholar had employed before. So new was this language that the sophisticated Imperial Ambassador in Venice described the Star Messenger as "a dry discourse or an inflated boast, devoid of all philosophy". 18 In contrast to Kepler's exuberant baroque style, some passages of the Sidereus Nuncius would almost qualify for the austere pages of a contemporary "Journal of Physics".
The whole booklet has only twenty-four leaves in octavo. After the introductory passages, Galileo described his observations of the moon, which led him to conclude:
"… 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 irregularities, uneven, full of hollows and protuberances, just like the surface of the earth itself, which is varied everywhere by lofty mountains and deep valleys."
He then turned to the fixed stars, and described how the telescope added, to the moderate numbers that can be seen by the naked eye, "other stars, in myriads, which have never been seen before, and which surpass the old, previously known stars in number more than ten times." Thus, for instance, to the nine stars in the belt and sword of Orion he was able to add eighty others which he discovered in their vicinity; and to the seven in the Pleiades, another thirty-six. The Milky Way dissolved before the telescope into "a mass of innumerable stars planted together in clusters"; and the same happened when one looked at the luminous nebulae.
But the principal sensation he left to the end:
"There remains the matter which seems to me to deserve to be considered the most important in this work, namely, that I should disclose and publish to the world the occasion of discovering and observing four planets, never seen from the very beginning of the world up to our own times."
The four new planets were the four moons of Jupiter, and the reason why Galileo attributed to their discovery such capital importance he explained in a somewhat veiled aside:
"Moreover, we have an excellent and exceedingly clear argument to put at rest the scruples of those who can tolerate the revolution of the planets about the sun in the Copernican system, but are so disturbed by the revolution of the single moon around the earth while both of them describe an annual orbit round the sun, that they consider this theory of the universe to be impossible."
In other words, Galileo thought the main argument of the anti-Copernicans to be the impossibility of the moon's composite motion around the earth, and with the earth around the sun; and further believed that this argument would be invalidated by the composite motion of the four Jupiter moons. It was the only reference to Copernicus in the whole booklet, and it contained no explicit commitment. Moreover, it ignored the fact that in the Tychonic system all the planets describe a composite motion around the sun and with the sun around the earth; and that even in the more limited "Egyptian" system, at least the two inner planets do this.
Thus Galileo's observations with the telescope produced no important arguments in favour of Copernicus, nor any clear committal on his part. Besides, the discoveries announced in the Star Messenger were not quite as original as they pretended to be. He was neither the first, nor the only scientist, who had turned a telescope at the sky and discovered new wonders with it. Thomas Harriot made systematic telescopic observations and maps of the moon in the summer of 1609, before Galileo, but he did not publish them. Even the Emperor Rudolph had watched the moon through a telescope before he had heard of Galileo. Galileo's star maps were so inaccurate that the Pleiades group can only be identified on them with difficulty, the Orion group not at all; and the huge dark spot under the moon's equator, surrounded by mountains, which Galileo compared to Bohemia, simply does not exist.
Yet when all this is said, and all the holes are picked in Galileo's first published text, its impact and significance still remain tremendous. Others had seen what Galileo saw, and even his priority in the discovery of the Jupiter moons is not established beyond doubt 18a ; yet he was the first to publish what he saw, and to describe it in a language which made everybody sit up. It was the cumulative effect which made the impact; the vast philosophical implications of this further prizing-open of the universe were instinctively felt by the reader, even if they were not explicitly stated. The mountains and valleys of the moon confirmed the similarity between heavenly and earthly matter, the homogeneous nature of the stuff from which the universe is built. The unsuspected number of invisible stars made an absurdity of the notion that they were created for man's pleasure, since he could only see them armed with a machine. The Jupiter moons did not prove that Copernicus was right, but they did further shake the antique belief that the earth was the centre of the world around which everything turned. It was not this or that particular detail, but the total contents of the Messenger from the Stars which created the dramatic effect.
The booklet aroused immediate and passionate controversy. It is curious to note that Copernicus' Book of Revolutions had created little stir for half a century, and Kepler's Laws even less at their time, while the Star Messenger, which had only an indirect bearing on the issue, caused such an outburst of emotions. The main reason was, no doubt, its immense readability. To digest Kepler's magnum opus required, as one of his colleagues remarked, "nearly a lifetime"; but the Star Messenger could be read in an hour, and its effect was like a punch in the solar plexus on those grown up in the traditional view of the bounded universe. And that vision, though a bit shaky, still retained an immense, reassuring coherence. Even Kepler was frightened by the wild perspective opened up by Galileo's spyglass: "The infinite is unthinkable," he repeatedly exclaimed in anguish.
The shock-waves of Galileo's message spread immediately, as far as England. It was published in March 1610; Donne's Ignatius was published barely ten months later, 19 but Galileo (and Kepler) are repeatedly mentioned in it:
I will write [quoth Lucifer] to the Bishop of Rome:
He shall call Galileo the Florentine to him ...
But soon, the satirical approach yielded to the metaphysical, to a full realization of the new cosmic perspective:
Man has weav'd out a net, and this net throwne
Upon the Heavens, and now they are his owne ...
Milton was still an infant in 1610; he grew up with the new wonders. His awareness of the "vast unbounded Deep" which the telescope disclosed, reflects the end of the medieval walled universe:
Before [his] eyes in sudden view appear
The secrets of the hoary Deep – a dark
Illimitable ocean, without bound,
Without dimension ... 20
6. The Battle of the Satellites
Such was the objective impact on the world at large of Galileo's discoveries with his "optick tube". But to understand the reactions of the small, academic world in his own country, we must also take into account the subjective effect of Galileo's personality. Canon Koppernigk had been a kind of invisible man throughout his life; nobody who met the disarming Kepler, in the flesh or by correspondence, could seriously dislike him. But Galileo had a rare gift of provoking enmity; not the affection alternating with rage which Tycho aroused, but the cold, unrelenting hostility which genius plus arrogance minus humility creates among mediocrities.
Without this personal background, the controversy which followed the publication of the Sidereus Nuncius would remain incomprehensible. For the subject
of the quarrel was not the significance of the Jupiter satellites, but their existence – which some of Italy's most illustrious scholars flatly denied. Galileo's main academic rival was Magini in Bologna. In the month following the publication of the Star Messenger, on the evenings of 24 and 25 April, 1610, a memorable party was held in a house in Bologna, where Galileo was invited to demonstrate the Jupiter moons in his spy-glass. Not one among the numerous and illustrious guests declared himself convinced of their existence. Father Clavius, the leading mathematician in Rome, equally failed to see them; Cremonini, teacher of philosophy at Padua, refused even to look into the telescope; so did his colleague Libri. The latter, incidentally, died soon afterwards, providing Galileo with an opportunity to make more enemies with the much quoted sarcasm: "Libri did not choose to see my celestial trifles while he was on earth; perhaps he will do so now he has gone to Heaven."
These men may have been partially blinded by passion and prejudice, but they were not quite as stupid as it may seem. Galileo's telescope was the best available, but it was still a clumsy instrument without fixed mountings, and with a visual field so small that, as somebody has said, "the marvel is not so much that he found Jupiter's moons, but that he was able to find Jupiter itself." The tube needed skill and experience in handling, which none of the others possessed. Sometimes, a fixed star appeared in duplicate. Moreover, Galileo himself was unable to explain why and how the thing worked; and the Sidereus Nuncius was conspicuously silent on this essential point. Thus it was not entirely unreasonable to suspect that the blurred dots which appeared to the strained and watering eye pressed to the spectacle-sized lens, might be optical illusions in the atmosphere, or somehow produced by the mysterious gadget itself. This, in fact, was asserted in a sensational pamphlet, Refutation of the Star Messenger, 20a published by Magini's assistant, a young fool called Martin Horky. The whole controversy about optical illusions, haloes, reflections from luminous clouds, and about the unreliability of testimonies, inevitably reminds one of a similar controversy three hundred years later: the flying saucers. Here, too, emotion and prejudice combined with technical difficulties against clear-cut conclusions. And here, too, it was not unreasonable for self-respecting scholars to refuse to look at the photographic "evidence" for fear of making fools of themselves. Similar considerations may be applied to the refusal of otherwise open-minded scholars to get involved in the ambiguous phenomena of occult seances. The Jupiter moons were no less threatening to the outlook on the world of sober scholars in 1610, than, say, extra-sensory perception was in 1950.
Thus, while the poets were celebrating Galileo's discoveries which had become the talk of the world, the scholars in his own country were, with very few exceptions, hostile or sceptical. The first, and for some time the only, scholarly voice raised in public in defence of Galileo, was Johannes Kepler's.
7. The Shield Bearer
It was also the weightiest voice, for Kepler's authority as the first astronomer of Europe was uncontested – not because of his two Laws, but by virtue of his position as Imperial Mathermaticus and successor to Tycho. John Donne, who had a grudging admiration for him, has summed up Kepler's reputation "who (as himselfe testifies of himselfe) ever since Tycho Brahe's death hath received it into his care, that no new thing should be done in heaven without his knowledge." 21
The first news of Galileo's discovery had reached Kepler when Wackher von Wackenfeld called on him on or around 15 March, 1610. The weeks that followed he spent in feverish expectation of more definite news. In the first days of April, the Emperor received a copy of the Star Messenger which had just been published in Venice, and Kepler was graciously permitted "to have a look and rapidly glance through it". On 8 April, at last, he received a copy of his own from Galileo, accompanied by a request for his opinion.
Galileo had never answered Kepler's fervent request for an opinion on the Mysterium, and had remained equally silent on the New Astronomy. Nor did he bother to put his own request for Kepler's opinion on the Star Messenger into a personal letter. It was transmitted to Kepler verbally by the Tuscan Ambassador in Prague, Julian de Medici. Although Kepler was not in a position to verify Galileo's disputed discoveries, for he had no telescope, he took Galileo's claims on trust. He did it enthusiastically and without hesitation, publicly offering to serve in the battle as Galileo's "squire" or "shield bearer" – he, the Imperial Mathematicus to the recently still unknown Italian scholar. It was one of the most generous gestures in the sour annals of science.
The courier for Italy was to leave on 19 April; in the eleven days at his disposal Kepler wrote his pamphlet Conversation with the Star Messenger in the form of an open letter to Galileo. It was printed the next month in Prague, and a pirated Italian translation appeared shortly afterwards in Florence.
It was precisely the support that Galileo needed at that moment. The weight of Kepler's authority played an important part in turning the tide of the battle in his favour, as shown by Galileo's correspondence. He was anxious to leave Padua and to be appointed Court Mathematician to Cosimo de Medici, Grand Duke of Tuscany, in whose honour he had called Jupiter's planets "the Medicean stars". In his application to Vinta, the Duke's Secretary of State, Kepler's support figures prominently:
"Your Excellency, and their Highnesses through you, should know that I have received a letter – or rather an eight-page treatise – from the Imperial Mathematician, written in approbation of every detail contained in my book without the slightest doubt or contradiction of anything. And you may believe that this is the way leading men of letters in Italy would have spoken from the beginning if I had been in Germany or somewhere far away." 22
He wrote in almost identical terms to other correspondents, among them to Matteo Carosio in Paris:
"We were prepared for it that twenty-five people would wish to refute me; but up to this moment I have seen only one statement by Kepler, the Imperial Mathematician, which confirms everything that I have written, without rejecting even an iota of it; which statement is now being reprinted in Venice, and you shall soon see it." 23
Yet, while Galileo boasted about Kepler's letter to the Grand Duke and his correspondents, he neither thanked Kepler nor even acknowledged it.
Apart from its strategical importance in the cosmological battle, the Conversation with the Star Messenger is without much scientific value; it reads like a baroque arabesque, a pattern of amusing doodles around the hard core of Galileo's treatise. It starts with Kepler voicing his hope that Galileo, whose opinion matters to him more than anybody's, would comment on the Astronomia Nova, and thereby renew a correspondence "laid aside twelve years ago". He relates with gusto how he had received the first news of the discoveries from Wackher – and how he had worried whether the Jupiter moons could be fitted into the universe built around the five Pythagorean solids. But as soon as he had cast a glance at the Star Messenger, he realized that "it offered a highly important and wonderful show to astronomers and philosophers, that it invited all friends of true philosophy to contemplate matters of the highest import... Who could be silent in the face of such a message? Who would not feel himself overflow with the love of the Divine which is so abundantly manifested here?" Then comes his offer of support "in the battle against the grumpy reactionaries, who reject everything that is unknown as unbelievable, and regard everything that departs from the beaten track of Aristotle as a desecration... Perhaps I shall be considered reckless because I accept your claims as true without being able to add my own observations. But how could I distrust a reliable mathematician whose art of language alone demonstrates the straightness of his judgement? ..."
Kepler had instinctively felt the ring of truth in the Star Messenger, and that had settled the question for him. However much he may have resented Galileo's previous behaviour, he felt committed "to throw himself into the fray" for Truth, Copernicus and the Five Perfect Solids. For, having finished the Promethean labours of the New Astronomy, he was again steeped in the mystic twilight of a Pythagorean
universe built around cube, tetrahedra, dodecahedra, and so on. They are the leitmotif of his dialogue with the Star Messenger; neither the elliptical orbits, neither the First nor the Second Law, are mentioned even once. Their discovery appeared to him merely as a tedious detour in the pursuit of his idée fixe.
It is a rambling treatise, written by a hurried pen which jumps from one subject to another: astrology, optics, the moon's spots, the nature of the ether, Copernicus, the habitability of other worlds, interplanetary travel:
"There will certainly be no lack of human pioneers when we have mastered the art of flight. Who would have thought that navigation across the vast ocean is less dangerous and quieter than in the narrow, threatening gulfs of the Adriatic, or the Baltic, or the British straits? Let us create vessels and sails adjusted to the heavenly ether, and there will be plenty of people unafraid of the empty wastes. In the meantime, we shall prepare, for the brave sky-travellers, maps of the celestial bodies – I shall do it for the moon, you Galileo, for Jupiter."
Living in an atmosphere saturated with malice, Professors Magini, Horky, and even Maestlin, could not believe their ears when they heard Kepler singing Galileo's praises, and tried to discover some hidden sting in the treatise. They gloated over a passage in which Kepler showed that the principle of the telescope had been outlined twenty years before by one of Galileo's countrymen, Giovanni Della Porta, and by Kepler himself in his work on optics in 1604. But since Galileo did not claim the invention of the telescope, Kepler's historical excursion could not be resented by him; moreover, Kepler emphasized that Della Porta's and his own anticipations were of a purely theoretical nature