There is every reason to welcome English translations of any of Kepler’s works, and in particular of his Somnium seu Opus posthumum de Astronomia Lunari (1634), which is not even available in the critical edition of Kepler’s works by Max Caspar and others, but only in the nineteenth-century edition of Frisch. Except for a recent edition of his Snowflake (Clarendon Press, 1966) and a translation (1965) by Edward Rosen of his Conversation With Galileo’s Sidereal Messenger (Dissertatio cum Nuncio Sidereo), neither of them major works, none of Kepler’s works has been completely translated into English; and his Latin is by no means easy. The Somnium was in the press when Kepler died in 1630. He had written the text of the dream itself in 1609, and it had circulated in manuscript. In about 1621 he began to annotate it copiously—the notes are four times as long as the text. It was published together with a letter to Paul Guldin, S.J., on lunar geography, and Kepler’s Latin translation of Plutarch’s On the Face in the Moon, also annotated, which unfortunately is not included in the translation under review.

Of all Kepler’s strange works this is one of the most bizarre. The interpretation of the main part of it presents few difficulties, and he stated clearly his chief motive for writing it. It gives a detailed picture of the universe as it would appear to a moon-dweller, together with conjectures about lunar climatic conditions, geography, and inhabitants; and, as Kepler states, “the object of my dream is to work out, through the example of the moon, an argument for the motion of the earth, or rather, to overcome objections taken from the general opposition of mankind,” that is, to break down the common-sense resistance to Copernicanism by making people realize that moon-dwellers would be equally convinced that their home was the stationary center of the universe. What is strange and mysterious is Kepler’s way of introducing his lunar astronomy. His dream, which he calls a fable, consisted of reading a book, which recounted the history of an Icelandic youth, Duracotus, whose mother, Fiolxhilde, was a witch. She sold him to the captain of a ship, which, fortunately, carried letters from an Icelandic bishop to the great Danish astronomer, Tycho Brahe, then living on the island of Hven. Duracotus studied astronomy there for five years, and then returned to Iceland, where his mother, by magic rites, summoned a spirit (daemon) of the moon. The daemon tells how, during lunar eclipses, he and his fellow spirits travel from the earth to the moon, sometimes taking with them some human, beings, but only thin and desiccated ones, old witches being especially suitable. After a short description of the journey, during which the human travelers are anesthetized, the daemon gives a long discourse on lunar astronomy and geography, that is, the straightforward scientific part of the work. Kepler’s notes on this introductory part are often as bewildering as the text—sometimes autobiographical, sometimes allegorical, sometimes irrelevantly factual. Duracotus certainly represents Kepler himself, who did study with Tycho Brahe, though not at Hven, and Kepler’s mother, probably partly in consequence of the Somnium, was arrested for witchcraft in 1615 and, largely through Kepler’s efforts, acquitted in 1621.

ALTHOUGH MR. LEAR and Mrs. Kirkwood are to be congratulated on their enterprise and courage in producing a translation and interpretation of this very interesting work, it must be stated that as an edition it is inadequate and as an interpretation lamentable. It should, I think, be a generally accepted principle that a scholar ought not to attempt the detailed interpretation of a text written in a language he does not know, especially if no previous work has been done on the text, and also that a minimum requirement for interpreting any one work of an author is to have read most, if not all, of his other works. Mr. Lear, who admits to knowing neither Latin nor German, has not therefore been able to read Kepler’s own words in the Somnium, nor to read any other of his works. The only aids he has had are the English translation of Max Caspar’s biography of Kepler and a few, not very happily chosen, modern works on the history of science. Caspar, though of course a fine scholar of Kepler, was sometimes a white-washing one, and moreover failed in his biography to give any references at all, so that it is quite useless as an instrument of scholarship. But even making allowances for these limitations, which should have deterred Mr. Lear from attempting the task, I find his interpretation of the Somnium often perversely wrong. He explains, for example, Kepler’s mysterious Introduction as a means of disguising his Copernicanism from dangerous reactionary theologians (“Kepler’s major objective was to spread word of Copernican science in a way that would not arouse enemies of science within the church”), whereas, in fact, as Mr. Lear could have learned from Caspar’s biography, Kepler throughout his life was openly and enthusiastically Copernican, as he was in the Astronomia Nova, published in the same year, 1609, as the Somnium was written. Equally grave doubts, though of a different kind, about Mr. Lear’s competence to interpret a work on lunar astronomy are aroused by the statement (p. 43) that Kepler learned from Plutarch’s On the Face in the Moon that Greek astronomers had discovered, among other facts about the moon, “that the phases of the moon were owing to the moon’s passage in and out of the shadow thrown by the earth as the earth moved round the sun.” This means, first, that the speakers in Plutarch’s dialogue were heliocentrists, but confused the phases with the eclipses of the moon, neither of which is true, and secondly, that Mr. Lear is a heliocentrist who confuses the phases with the eclipses of the moon, which must, I fear, be true.


THE MAIN FAULT of Kepler’s Dream as an edition is the failure to provide any annotation at all; Kepler’s own notes are quite as much in need of explanation as his original text. This failure has often resulted in the translation being worse than it need have been. For example, Kepler in a note on Fiolxhilde’s demons stated that they were “non spiritus illi apostatae et nequam, quibus est cum magis et sagis commercium, qui suae crudelitatis et noxarum testimonium habent irrefutabile a proprio suo patrono Porphyrio,” which is translated as: “They are not those wicked and good-for-nothing spirits with whom witches and fortunetellers have dealings, who give irrefutable proof of their cruelty in the identity of their patron, Porphyry.” If anyone had bothered to look up Porphyry, he would have found that in Book II of his De Abstinentia he devoted several chapters to the evil-doings of bad demons, that he was an anti-Christian polemicist, and that he and his disciple Iamblichus were the main inspiration of the Emperor Julian the Apostate; which facts would have led to the correct translation: “not those apostate and wicked spirits [i.e. fallen angels], who have commerce with magicians and fortune-tellers, and who have irrefutable witness to their cruelty and crimes from their own patron, Porphyry.” Or again, when Kepler is giving various reasons he may have had for saying that the moon-demon was summoned by twenty-one characters, we read in this translation: “It amuses me too that such is the number of possible throws of dice. For 21 is a triangular number, with a base of 6.” If the translator had had to write a note explaining what triangular numbers are, she would have been led to reflect on the possible combinations of six-sided dice, and thus to notice that Kepler had in fact written: “throws of two dice.” Apart from such slips however the translation is on the whole faithful, though, with such a difficult writer as Kepler, I think it highly desirable that the original text should be given as well, as it is in the edition of the Snowflake mentioned above.

I am dwelling at length, and perhaps unkindly, on the faults of this book because I find it very disturbing that it should have been accepted and published by a university press. The standards of historical scholarship have always been regrettably vague and precarious; but on the whole universities have at least attempted to maintain a high standard. It looks now as if this tradition is crumbling, and I therefore think it right to protest, even at the cost of appearing pedantic and unduly severe.

ANOTHER REASON for protest is that Mr. Lear’s interpretation exemplifies, in a grotesquely extreme form, an approach to the history of science which is still widespread, though rightly becoming more and more discredited. This approach consists of picking out cases where an earlier scientist agrees with a modern textbook of the science in question and giving him a pat on the back for being right; cases where he does not agree are either ignored, or explained away, or anxiously excused, or contemptuously censured; his religious and philosophical convictions are considered entirely irrelevant. This kind of “history” is peculiarly misleading when applied to Kepler, whose still valid planetary laws were for him comparatively unimportant by-products of the stupendous religious achievement of having demonstrated that nothing in the solar system was arbitrary, that God the supreme geometer had created everything in the most beautiful manner possible, that every apparent irregularity in the planetary orbits and movements could be accounted for by a combination of the two great interconnected principles of the Platonic regular solids and the proportions of musical consonances, and that all this complicated beauty was centered on, and governed by, the sun, for “Deus in sole posuit tabernaculum suum” (“God has placed his tabernacle in the sun”—it pleases me that Kepler knew that this is a mistranslation of Psalm XIX, 4, but thought that St. Jerome was divinely inspired in making it). Moreover, there is really no excuse for subjecting Kepler to this pat-on-the-back history so long after the admirable studies of E. A. Burtt, A. Koyré, and others, who have shown in Kepler the fascinating and complicated combinations of mathematics with a mystical religion, of a wild, almost demented imagination with an unfailing respect for empirical fact, of a subtly critical mind with almost childish credulity. Instead of this rich, living complexity Mr. Lear presents us with a hard-headed modern scientist fighting against medieval metaphysics and superstitions, and being “prescient” about space-travel, a Kepler who disbelieves in astrology (p.78) and witchcraft (p.36), and who believes in an infinite universe (p.17). Kepler is allowed, indeed encouraged to believe in space-travel, because we have nearly achieved it; but, because we think the moon is uninhabited, his carefully worked-out conjecture that the craters on the moon are cities is dismissed (p.20) as “a satire on the Aristotelian search for final cause [sic].”


That Kepler believed in the existence of witches is clear from the note to the Somnium about demons, quoted above, and from another note (n.60) it is also clear that he thought it equally likely or unlikely that witches could fly through the air and that men could travel to the moon. As a good Neoplatonist, let alone Christian, Kepler of course took evil daemones seriously, as one can see from his commentary on Proclus’s Hymn to the Sun in the last chapter of the Harmonice Mundi, though the demons in the Somnium appear to be only allegorical. He was also interested in good spirits, especially in guardian angels, and discusses at length whether their failure sometimes to function is due to their clients’ sins or to astrological causes.

THAT KEPLER practised astrology and published long defenses of it is too well-known for me to need to labor the point. His astrology, like Bacon’s astrologia sana, was a reformed one, and, like most philosophic astrologers of the Renaissance, he disapproved of any attempt to make precise, detailed predictions, and criticized contemporary astrological practice as being full of vanity and superstition. By reducing all astral influences to the effects of certain aspects, that is, of certain angles made by any two planets’ rays meeting on the earth, he connected his astrology with his musical consonances. The same simple ratios govern both, and are perceived instinctively by the soul of the earth and by the lower soul in man. But Kepler’s astrology also had an empirical basis; for many years he kept careful records of the weather (controlled by the soul of the earth); these led him, unwillingly, to the conclusion that the ratios of the effective aspects were not identical with the seven musical consonances, and his respect for facts made him alter and extend his whole system of harmonies and aspects. Coupled with this strict empiricism one finds in his defenses of astrology the strangest bursts of imagination and examples of credulity. The Tertius Interveniens (1610), for example, begins with a long drawn out analogy between marriage and astrology: Just as marriage, since the Fall, is always stained with lust and adultery, but nevertheless is a Godgiven institution that still serves the good purpose of carrying on the human race, so astrology, contaminated though it is with superstition and impious curiosity, can produce useful predictions of a general kind. In developing this analogy, Kepler points out that bastards, though the product of sin, may yet be virtuous citizens, and so may even the products of worse sins than fornication; he then quotes (without acknowledgement) in all seriousness the following charming story (“ein sehr gedenckwürdiges Exempel“) from Martin Del Rio’s Disquisitiones Magicae: In Belgium there was a wicked man who had intercourse with a cow, which after a few months gave birth to a male human child; the child was baptized and grew up to be extremely pious, devoting himself mainly to works of penitence on behalf of his father, but retaining, however, some bovine propensities, such as grazing and chewing the cud.

That Kepler believed that the moon was inhabited is not only evident from the Somnium and the Dissertatio cum Nuncio Sidereo, but also it is clear from the Harmonice Mundi that he believed the other planets to be inhabited, above all the sun, to which was directed the divine polyphonic music of the planets, intelligible but soundless—“annon vel sensus ipsi exclamant, ignea hic habitare corpora, Mentium simplicium capacia…? (“Do not even our senses cry out to us that here live fiery bodies endowed with pure intellects..?”).

All this is not much help in explaining the enigmas of the Introduction to the Somnium, but it does suggest the qualifications necessary to perform this task. What we need is an edition annotated by a scholar who has not only mastered Renaissance astronomy and mathematics, but also Kepler’s Latin (and German) style, who is not only familiar with the Neoplatonic tradition, but also with the strange imagination of this great thinker and with his frequent, bewildering jocularity, and, above all, who has the historical sense and the humility not to despise now obsolete beliefs.

This Issue

September 22, 1966