Joannes Kepler 1571-163o

BY PROFESSOR H. DINGLE

[Our regular series" Science, Yesterday and To-day" has been held over for ono week to allow us to publish the following article, by the Hon. Serzetary of the Royal Astronomical Society. Next week Professor Julian Huxley will write on" Recent Progress in Biology." Professor Carr-Saunders' article on Sociology, which was to have appeared this week, will appear in our issue of November 29th.] rimmEE hundred years ago one of the greatest of the 1 world's astronomers died in poverty and neglect at Ratisbon, and on November 15th the little German town of Weilderstadt, in which be was born, will witness a memorable sight. Not, indeed, a rare one, for Germany honours its great men now, and the statue of Kepler in the market-place of Weilderstadt has received many a tribute from modern Germans to one of whom their fathers were not worthy. The writer has a vivid remembrance of such an event just over two years ago, when the Astronomische Gesellschaft, then meeting at Heidelberg, made a pilgrimage southwards to render homage to their great predecessor. The quaint little town, still whispering the last enchantments of the Middle Age, -seemed strangely to unite the mediaeval and the modern, and little imagination was needed to feel the spirit of Kepler brooding over the place—" a presence which was not to be put by."

For Kepler, more than any of the great men of this epoch who ushered in the age of science, harmonized in himself the essential elements of the old and the new ages. Copernicus kept himself too far aloof from the world to inspire in us much more than an academic sympathy. In Tycho Brahc the crassest superstition of the dark ages cohabited with an ultra-modern recognition of the importance of exact measurenient, but they held no intercourse ; it was a Box-and-Cox-like association which leads us to regard Tycho as almost a dual per tonality. The miracle that was Galileo, on the other hand, sprang fully developed from the brain of pure science—an immaculate conception almost without parallel in the history of transition movements. But Kepler—mystic, philosopher, scientist, artist—what for- mula can describe the man whose scientific investigation was religious devotion, to whom observations were sacred, and who would yet refuse to consider a natural interpretation of them if it appeared inharmonious ?

There run through all Kepler's works, as inseparable threads of their texture, the search, familiar to the scientist of to-day, for rational co-ordination of observa- tions, and the almost infinite remoteness of a mysticism with which we have lost touch. Even the clearest of his writings is hardly intelligible to us in its completeness on this account. Take, for example, his remarks on the question whether traditional authority or sensory evidence should form the basis of our rationalizing, which was pre-eminently the question at issue in the early seven- teenth century :—

" Now as touching the opinions of the Saints about these natural points. I answer in one word, That in Theology, the weight of Authority, but in Philosophy the weight of Reason is to be con- sidered. Therefore Sacred was Lactantius, who denyed the Earth's rotundity ; Sacred was Augustine, who granted the Earth to be round, but denyed the Antipodes ; Sacred is the Liturgy of our Moderns, who admit the smannesse of the Earth, but deny its Motion : But to me more sacred than all theseIs Truth, who with respect to the Doctors of the Church, do demonstrate from Philosophy that the

Earth is both round, eirctunbabited by -Antipodes, of a most con- temptible smallness° and in a word, that it is ranked amongst the Planets."

Who else could give us such a reconciliation as this ?

Kepler was born in 1571, a premature, sickly child, into a household torn asunder by violent quarrels. Illness and family misfortunes robbed him of all but the most fragmentary education in his boyhood, but an eager spirit triumphed over all obstacles, and he obtained the degree of Master at the University of Tubingen in his twentieth year. Three years later the Chair of Astronomy at Gratz fell vacant, and Kepler, with little knowledge of astronomy and no enthusiasm for it, was forced, as lie tells us, to accept the position by the authority of his tutors.

" Not that I was alarmed . . . by the remoteness of the situation, but by the unexpected and contemptible nature of the office and bv the slightness of my information in this branch of philosophy. entered on it, therefore, better furnished with talent than Imow- ledge ; with many protestations that I was not abandoning my claim to be provided for in some other more brilliant profession."

Not a very promising beginning, but a change was imminent. No sooner had he set himself to master his subject than the divine madness seized him, and thence- forth the course of Kepler's life was marked out. He was possessed by the passion of reading the thoughts of God in His handiwork, the heavens. The Pythagorean music of the spheres was not for the sensual ear, but for the ear of the mind, and no one had yet heard it : he would be the first. He thereupon set himself one gigantic task after another, testing possible ideas by comparison with the observations of Tycho, whose assistant he soon became. Any idea that appealed to his sense of harmony was examined and thoroughly tested, however improbable it might appear in the cold light of reason. Would it require years of incessant labour ? No matter : amid poverty, family troubles, illness, religious persecution, and failure after failure, he followed with undiminishing zeal and constant prayer the path which he had chosen. He knew instinctively that Truth was Beauty, but he learned by bitter experience that Beauty might not be Truth.

The mind of Kepler is well illustrated by an anecdote which he gives us in a refutation of the opinion of the Epicureans that a new star which appeared in the year 1604 was a fortuitous concourse of atoms.

" I will tell these disputants, my opponents, not my own opinion, but my wife's. Yesterday, when weary with writing, and my mind quite dusty with considering these atoms, I was called to supper, and a salad I had asked for was set before me. ' It seems, then,' raid I aloud, that if pewter dishes, leaves of lettuce, grains of salt, drops of water, vinegar, and oil, and slices of egg, had been flying about in the air from all eternity, it might at last happen by chance that there would come a salad.' Yes,' says my wife, but not so nice and well dressed as this of mine is.' "

Here we have the essence of Kepler. It was not the salad, but the well dressed salad that spoke of the divine Mind. Any monster could make suns and planets, but only God could give them a plan.

After eight years Kepler gave to the world two of the three laws which now bear his name. These laws assert that the planetary orbits are ellipses, and state how the speed of a planet varies as it approaches or recedes from the Sun. Further toil followed, and seventeen years after the beginning of his labours he discovered the third law. In his book, The Harmonies of the World, he tells us the circumstances of the discovery.

" what I prophesied two and twenty years ago . . What I firmly believed long before I had seen Ptolemy's Harnitmies—what I had promised my friends in the title of this book, which I named before I was sure of my discovery—what sixteen years ago I urged as a thing to be sought—that for which I joined Tycho Brahe, for which I settled in Prague, for which I have devoted the beet part of my life to astronomical contemplation, at length I have brought to light and recognized its truth beyond my most sanguine expecta- tions. It is not eighteen months since I got the first glimpse of light, three months since the dawn, very few days since the unveiled Sun, most admirable to gaze upon, burst upon me. . . . For, after

I had by unceasing toil through a long period of time, using the observations of Braise, discovered the true distances of the orbits, at last, at last, the true relation of the periodic times to the orbits and, if you ask for the exact time, . . . though late, yet looked upon me idle And after long time came ;

conceived on the 8th of March of this year, 1618, but unsuccessfully brought to the test and for that reason rejected as false, but, finally returning on the 15th of May, by a new onset it overcame by storm the shadows of my mind, with such fullness of agreement between my seventeen-years' labour on the observations of Brahe and this present study of mine that I at first believed that I was dreaming and was assuming as an accepted principle what was still a subject of enquiry. But the principle is unquestionably true and quite exact; the periodic times of any two planets are to each other exactly as the cubes of the aware roots of their median distances."

What an anti-climax it seems : the frenzy of a poet over a formal algebraic proposition. But we shall not understand Kepler unless we realise that it was no anti- climax but the most glorious of culminations, beside which the rapture of a Keats over a nightingale is but a casual emotion. For this law, unlike the others, shows a relation not merely between the characteristics of a single plan- etary orbit, but between all the orbits of the solar system. For the first time in the history of the world it was seen that they were a system, and he, Joannes Kepler, was the first of mortal men to think again the thoughts of God at the creation.

" Nothing holds me,' he goes on, ` I will indulge my sacred fury ; I will triumph over mankind by the honest confession that I have stolen the golden vases of the Egyptians to build up a tabernacle for my God far away from the confines of Egypt. If you forgive me, I rejoice ; if you are angry, I can bear it ; the die is cast, the book is written, to be read either now or by posterity, I care not which ; it may well wait a century for a reader as God has waited 6,000 years for an observer.' "

How evasive is the line between genius and stupidity ! Had Kepler failed, his name, if it had come down to us at all, would have become a symbol of the futility of arbi- trary guessing. Wherein, then, lies his greatness ?

I think it is in the steadfastness with which, in an age when fanciful speculation was still the dominant intellec- tual habit, he rejected one after another his fondest hopes because they could not be reconciled with the observations of Tycho Brahe. How easy it is for a theorist to ascribe apparent discrepancies in his work to errors of observ- ation, even when the observations are his own, is well known to modern investigators. How much easier, then—almost overpoweringly so—must it have been in a speculative age, when the observations were those of another long dead and success was the passion of one's life. It is by his unswerving loyalty to Truth that Kepler commands our homage, and not forgetting the daring imagination of Copernicus and the magnificent intellect of Galileo, we feel unable to quarrel with Brewster when lie places Kepler next to Newton in the hierarchy. of great men. His three laws of planetary motion have been the guidance of three centuries of research, and without them the great work of Newton would have been impossible, but it is the glory of Kepler that the man transcends the achievement. His work has brought him recognition, but it is he whom primarily we recognize.