Indeed, a painful and perturbed life fell to the lot of Kepler. The most crushing poverty all his life oppressed him. For, though his nominal salary as Astronomer Royal was large enough, yet the treasury was so exhausted that it was impossible for him ever to obtain more than a pittance. What a sad tragedy do these words, in a letter to Mästlin, reveal:—"I stand whole days in the antechamber, and am nought for study." And then he adds the sublime compensation: "I keep up my spirits, however, with the thought that I serve, not the Emperor alone, but the whole human race,—that I am laboring not merely for the present generation, but for posterity. If God stand by me and look to the victuals, I hope to perform something yet." Eternal type of the consolation which the consciousness of truth brings with it, his ejaculation on the discovery of his third law remains one of the sublimest utterances of the human mind:—"The die is cast; the book is written,—to be read now or by posterity, I care not which: it may well wait a century for a reader, as God has waited six thousand years for an observer!" Cast in a stormy and chaotic age, he was persecuted by both Protestants and Catholics on account of the purity and elevation of his religious ideas; and from the disclosures of Baron von Breitschwert [1] it seems, that, in the midst of his sublimest labors, he spent five years in the defence of his poor old mother against a charge of witchcraft. He died in 1630, in his sixtieth year, (with the prospect of starvation before him,) of a fever which he caught when on a journey to Ratisbon, whither he had gone in the attempt to get part of his pay!
[Footnote 1: Johann Keppler's Leben und Wirken: nach neuerlich aufgefundenen Manuscripten bearbeitet. Stuttgart, 1813.]
In what bewildering and hampering environment he found himself with the "Tübingen doctors" and the "Würtemberg divines," his letters reveal. On the publication of the "Prodromus," Hafenreffer wrote to warn him:—"God forbid you should endeavor to bring your hypothesis openly into argument with the Holy Scriptures! I require of you to treat the subject merely as a mathematician, and to leave the peace of the Church undisturbed." To the Tübingen doctors he replied:—"The Bible speaks to me of things belonging to human life as men are used to speak of them. It is no manual of Optics or of Astronomy; it has a higher object in view. It is a culpable misuse of it to seek in it for answers on worldly things. Joshua wished for the day to be lengthened. God hearkened to his wish. How? This is not to be inquired after." And surely the long-vexed argument has never since unfolded better statement than in the words of Kepler:—"The day will soon break when pious simplicity will be ashamed of its blind superstition,—when men will recognize truth in the book of Nature as well as in the Holy Scriptures, and rejoice in the two revelations." [1]
[Footnote 1: Harmonices Mundi.]
On this avowal he was branded as a hypocrite, heretic, and atheist.
To Mästlin he wrote:—"What is to be done? I think we should imitate the Pythagoreans, communicate our discoveries privatim, and be silent in public, that we may not die of hunger. The guardians of the Holy Scriptures make an elephant of a gnat. To avoid the hatred against novelty, I represented my discovery to the Rector of the University as a thing already observed by the ancients; but he made its antiquity a greater charge against it than he could have made of its novelty."
And, indeed, the devotion to truth in that age, as in others, required an heroic heart. Copernicus kept back the publication of his "De Revolutionibus Orbium Caeslestium" for thirty-six years, and received a copy of it only on his death-bed. Galileo tasted the sweets of the Inquisition. Tycho Brahe was exiled. And Kepler himself was persecuted all his life, hounded from city to city. And yet the sixteenth century will ever be memorable in the history of the human mind. The breaking down of external authority, the uprise of the spirit of inquiry, of skepticism, and the splendid scientific conquests that came in consequence, inaugurated a mighty movement which separates the present promises of mankind from all past periods by an interval so vast as to make it not merely a great historical development, but the very birth of humanity. While Tycho Brahe, at the age of fifty-four, was making his memorable observations at Prague, Kepler, at the age of thirty, was applying his fiery mind to the determination of the orbit of Mars, and Galileo, at thirty-six, was bringing his telescope to the revelation of new celestial intervals and orbs. Within the succeeding century Huygens made the application of the pendulum to clocks; Napier invented Logarithms; Descartes and Galileo created the analysis of curves, and the science of Dynamics; Leibnitz brought the Differential Calculus; Newton decomposed a ray of light, and synthesized Kepler's Laws into the theory of Universal Gravitation.
Into this age, when the Old and New met face to face, came the questioning and quenchless spirit of Kepler. Born into an age of adventure, this new Prometheus, this heaven-scaler, matched it with an audacity to lift it to new reaches of realization.
A singular naiveté, too, marked this august soul. He has the frankness of Montaigne or Jean Jacques. He used to accuse himself of gabbling in mathematics,—"in re mathematica loquax,"—and claimed to speak with German freedom,—"scripsi haec, homo Germanicus, more et libertate Germanica." He marries far and near, brings planetary eclipses into conjunction with pecuniary penumbras, and his treatise on the perturbations of Mars reveals equal perturbations in his domestic economy. It may be to this candor, this gemüth, that we are to ascribe the powerful personal magnetism he exercises in common with Rousseau, Rabelais, and other rich and ingenuous natures. Who would be otherwise than frank, when frankness has this power to captivate? The excess of this influence appears in the warmth betrayed by writers over their favorite. The cool-headed Delambre, in his "Histoire de l'Astronomie," speaks of Kepler with the heat of a pamphleteer, and cannot repress a frequent sneer at his contemporary, Galileo. We know the splendor of the Newtonian synthesis; yet we do not find ourselves affected by Newton's character or discoveries. He touches us with the passionless love of a star.
Kepler puts the same naiveté into his speculative activity, with a subtile anatomy laying bare the metaphysique of his science. It was his habit to illumine his discoveries with an exhibition of the path that led to them, regarding the method as equally important with the result,—a principle that has acquired canonical authority in modern scientific research. "In what follows," writes he, introducing a long string of hypotheses, the fallacy of which he had already discovered, "let the reader pardon my credulity, whilst working out all these matters by my own ingenuity. For it is my opinion that the occasions by which men have acquired a knowledge of celestial phenomena are not less admirable than the discoveries themselves." His tentatives, failures, leadings, his glimpses and his glooms, those aberrations and guesses and gropings generally so scrupulously concealed, he exposes them all. From the first flashing of a discovery, through years of tireless toil, to when the glorious apparition emerges full-orbed and resplendent, we follow him, becoming party to the process, and sharing the ejaculations of exultation that leap to his lips. Seventeen years were required for the discovery of the harmonic law, that the squares of the times of the planetary revolutions are proportional to the cubes of their mean distances; and no tragedy ever equalled in affecting intensity the account he has written of those Promethean years. What rays does he let into the subtile paths where the spirit travels in its interrogations of Nature! We should say there was more of what there is of essential in metaphysics, more of the structural action of the human mind, in his books, than in the concerted introspection of all the psychologists. One sees very well that a new astronomy was predicted in the build of that sky-confronting mind; for harmonic ratios, laws, and rhymes played in his spheral soul, galaxies and gravitations stretched deeper within, and systems climbed their flaming ecliptic.