Before entering on any details relating to Galileo’s life and works, I propose to give a brief sketch of the progress of astronomical knowledge up to his time; for without this, one cannot appreciate correctly the value of his contributions to science, a value exaggerated or underrated by different writers, each according to his respective bias.

The primitive conception of the Earth as a vast plain with the ocean flowing round it, and the solid firmament in the sky above it, with the Sun, Moon, and Stars driven across by some mysterious agency, need not be noticed from an astronomical point of view; it appeared naturally in ancient poetry and in the forms of speech adopted and continued by popular usage; but it is not necessary to dwell upon it.

The first astronomers with whom we are acquainted were the Greeks, though it is said by some writers that the Chaldeans and Egyptians were really the original astronomers of the ancient world, and what the Greeks knew was borrowed from them.

The vast majority of men from the earliest times down to the birth of Galileo believed that the Earth was the centre of the universe, round which the Sun, Moon, and Stars revolved every twenty-four hours; round which, also (as careful observers had perceived), the Sun had an annual motion, progressing through the various signs of the zodiac; moreover, it had been noticed that the planets moved round the Earth, though at widely differing periods.

Yet there had been some few men, exceptionally gifted, who had guessed (and truly so) that the popular conception was a wrong one. It is said that the old Greek philosopher, Pythagoras, taught his disciples that the Sun was the real centre of our system, and that the Earth and planets circulated round it; but he does not seem to have openly and explicitly published his doctrine, though the tradition of his having so taught has always existed. If he taught it, however, he stands almost alone among the ancients. There were two great authorities in particular, whose opinion carried immense weight, and who were both decided in holding that the Earth was the centre, and the Sun a revolving planet. The first of these, Aristotle, has exercised an influence over succeeding generations which is simply marvellous. How vast was the weight of his name as a philosopher in the age of the schoolmen is well known to every one who has ever glanced at the greatest work of the greatest intellect of that age, the “Summa” of St. Thomas Aquinas. This celebrated writer quotes him as “philosophus,” in his opinion the philosopher par excellence, and besides his general appreciation of him as thus shown, he wrote an elaborate treatise on the “Astronomy” of Aristotle.

Nor has this influence been confined to the schoolmen; it has remained ever since, even to this day and in this country, where in the University of Oxford his great work on ethics is still a standard book of study. At the time of Galileo, such was the reverence felt towards his authority in Italy and in Rome, that the Peripatetici, as those who specially belonged to his school were called, were probably quite as indignant with the revolutionary astronomer for disregarding the teaching of their philosopher, as for going counter to the literal interpretation of Scripture.

But in pure astronomy, apart from all other philosophy, the greatest of all ancient writers was Ptolemy, who in the second century of the Christian era wrote a work called the “Almagest,” which is a complete compendium of the science as known at that date. Ptolemy probably borrowed very much from his great predecessor, Hipparchus, who has been called the father of astronomy, and who was the first to discover—to take a remarkable instance—the phenomenon known as the precession of the equinoxes, involving as it does the difference in length between the solar and sidereal years. The system of Ptolemy was briefly this: The heavens and the Earth are both spherical in form—the Earth being immovable in the centre, and all the heavenly motions taking place in circles. For this he gives his reasons—sound and good reasons for the spherical shape of the Earth; unsound and mistaken, however, for the denial of the Earth’s rotation on its axis, an opinion he evidently knew had been maintained by some persons; one important argument on this latter head being that if the Earth rotated with the great velocity necessary to carry it round in one day, it would leave the air behind it. He places the Earth (as already said) in the centre, then the Moon as the nearest planet revolving round it, the next Mercury, then Venus, then the Sun, and beyond these Mars, Jupiter, and Saturn. All moved in circles, but since, with the exception of the Sun and Moon, simple circles would not account for the motions, he supposes small circles in a retrograde direction forming loops upon the main circle, which he calls epicycles; undoubtedly following in this respect, Hipparchus, who three centuries before had struck out the same idea. It is curious that Ptolemy’s arguments (as above mentioned) show clearly that in his day there were some persons, though their names have perished,1 some one or two philosophers endowed with a marvellous insight into Nature, who had guessed at the true solution of the great astronomical problem; but they left no enduring mark on their age. The system of Ptolemy accounted for all the phenomena of the heavenly bodies that could be observed without the use of the telescope; naturally it held undisputed sway for many generations.

The first writer who revived the doctrine of Pythagoras as to the Earth’s movement (if, indeed, Pythagoras ever really taught it) was Nicholas de Cusa; he was a German by birth, having, in fact, been born at TrÈves, in 1401; but he was educated in Italy. He rose to a high ecclesiastical position, and was created cardinal by Pope Eugenius IV., in 1448; his book just alluded to was entitled “De Docta Ignorantia,” and was dedicated to Cardinal Cesarini.

The first, however, whose work obtained any great notoriety, and who upheld the doctrine that the Earth revolved around the Sun, was Nicholas Kopernik, commonly called by the Latinised form of his name, Copernicus. He, too, was a German, born at Thorn, in 1473; he studied for a time at the University of Cracow, and like Nicholas de Cusa, afterwards in Italy, and was subsequently raised to the ecclesiastical dignity of a Canon. It is probable that he was not a priest (though he is frequently spoken of as such), but a Canon in minor orders. In 1500 he was appointed professor of mathematics at Rome; and such was his scientific reputation that he was consulted by the Council of Lateran, held in 1512, on the question of the reform of the calendar—a reform carried out at a later period by Pope Gregory XIII.

The system of Copernicus was well received at Rome. A German disciple of his, John Albert Widmanstadt, in the year 1533, expounded it before Pope Clement VII., and produced a very favourable impression. Nor was the favour shown to Copernicus and his teaching ever withdrawn at Rome; his great work, “De Revolutionibus Orbium Coelestium” (published, it is said, by the advice of Cardinal Schunberg, Bishop of Capua), was dedicated to the reigning Pope, Paul III.; nor does he appear to have received at any time the least rebuke or discouragement from the Holy See; he died, however, immediately after the printing of his book, in May, 1543.

Copernicus supposed the heavenly bodies, the Earth included, to revolve round the Sun in circles; but, as it was evident that they did not exactly do this, he used the theory of epicycles, and supposed each planet to make two revolutions in each epicycle for every revolution round the Sun. The true solution of the difficulty was due to Kepler, who lived in the next century, and who discovered that the planets moved in ellipses. Copernicus held, and, of course, held truly, that the Earth revolves on its axis, thereby causing the apparent diurnal motion of all the heavenly bodies from east to west.

Owing to his work having been the first of any great importance that maintained argumentatively the system called heliocentric, that is to say, in which the Sun is the real centre, round which the planets, including the Earth, revolve—for the treatise of Nicholas de Cusa does not appear to have had any extensive circulation—it is usual to speak of this system as the Copernican one, notwithstanding the errors from which its great author was unable to extricate himself, and which have long since been rectified by subsequent writers; so that even at this day we retain the name.

It is always useful in scientific subjects to introduce a definition; and this is my definition of the sense in which I employ the word Copernican, that it is simply as opposed to the system in which the Earth is the centre of the visible universe, and the Sun revolving about it. It is, in fact, less accurate but more convenient than the employment of the Greek words heliocentric and geocentric to denote the two systems. Greek words, no doubt, abound in our scientific vocabulary, as the following plainly show: astronomy, geology, geography, barometer, thermometer, microscope, telescope; but these have become naturalised in our language by long use, which heliocentric and geocentric have not as yet been.

After Copernicus there arose an astronomer of great merit, a Dane, Tycho BrahÉ by name, who attempted to start a fresh system—a modification, in fact, of that of Ptolemy. He made all the planets revolve round the Sun, and the Sun, accompanied by the planets, round the Earth. He deserves great credit for his painstaking observations; but he lived just before the invention of the telescope—or, at least, before it was used for astronomical purposes—and, therefore, was under an infinite disadvantage. His chief objection to the system of Copernicus was one at which a modern astronomer would smile, but which in those days seemed very weighty—namely, the enormous distance at which you must suppose the fixed stars to be situated, if it were true. The philosophers of that age did not like to admit such a waste of space as that which must intervene between the orbit of Saturn and the stars. And, on the Copernican theory, if the stars were not situated at an immense, almost infinite distance, they ought to appear to move in a way they certainly do not. Tycho BrahÉ was born in 1546. His theory never made much way; it had not, I imagine, sufficient elements of probability to recommend it generally; while the subsequent invention of the telescope, and the works of Kepler and Galileo, coming so soon after Tycho BrahÉ, prepared the way for that almost universal reception of the Copernican system which we have since witnessed. I shall refer later on to Tycho and his observations.

Such, then, was the state of astronomical theories in the latter part of the sixteenth century. Enlightened men like Copernicus had guessed—not accurately, it is true, but with a considerable approach to accuracy—at the real facts of the case. Tycho BrahÉ (who, I suspect, would have been converted to Copernicanism if his life had been prolonged) had suggested a system of compromise not likely, in the long run, to satisfy any thoughtful mind; while the bulk of men, even the learned, adhered to the old Ptolemaic scheme. Something, however, now occurred which was destined to work, sooner or later, a complete revolution in astronomy. The telescope was invented, and, at the same time, there arose a man who knew how to use it: that man was Galileo. He was not the inventor of it, for it was first constructed in Holland or Belgium; yet he had the energy and the skill to make a telescope, without having previously seen one, simply from the account he had heard of the instrument. The telescope that he constructed, which still bears his name, was the simplest possible. It was of a form now disused excepting for opera-glasses and for the far more powerful binocular field-glasses with which we are so familiar; but for telescopes properly so called an improved principle has long since been introduced. Galileo was the first man that ever, so far as we know, turned the telescope upon the heavens. How he was rewarded for his pains we shall presently see; and I propose to introduce a narrative of the principal events in his life, since there are no means for forming a judgment so valuable as having the facts of the case clearly before the mind.

For most of the facts I am indebted to M. Henri de l’Épinois, whose elaborate article in the French publication known as La Revue des Questions Historiques is of the highest value; as the author of this article has done what I suspect very few writers on Galileo have even attempted to do, namely, to inspect the documents preserved in the Vatican bearing on the process, some of which he gives at full length. Not having myself had the same advantage, I yet feel that I am treading on safe ground when I take my facts from M. de l’Épinois; for there is scarcely a statement that he makes for which he does not give his authority, whether from the documents just mentioned, or from Galileo’s own letters, or from other trustworthy evidence.2

To treat of Galileo, and to pass over the events which brought him into collision with the ecclesiastical authorities, would of course be impossible, nor is it easy to touch upon these matters without having some standpoint of one’s own—some principle to guide one, some basis from which to argue. I do not shrink from stating that I write from a Catholic standpoint; but without entering minutely into those subtle questions which are the province of the trained theologian.

As, however, a good deal of the narrative is connected with the action of the Roman Congregations, as they are termed, it may not be superfluous to explain briefly the nature of these institutions. They are formed by the selection of certain Cardinals, one of them acting as Prefect of the Congregation, to whom are added other ecclesiastics as consultors and as secretary. The Congregation of the Index, to which reference will hereafter be made, was instituted not long after the Council of Trent, by Pope St. Pius V., and has for its duty, as its name implies, the pointing out to the faithful people such books as they ought to abstain from reading. The chief consultor of the Index is the “Master of the Apostolic Palace,” whom I shall have occasion to mention more than once in connection with that Dialogue of Galileo which brought him into such serious disgrace at Rome.

The Congregation of the Inquisition—I need hardly say, not to be confounded with the Spanish tribunal of that name, which was founded at an earlier period, nor with similar tribunals in other countries—was erected in 1542 by Pope Paul III., and besides the other officials attached to it, had certain theologians called “qualifiers,” whose duty it was to give an opinion to the Congregation on questions submitted to them.

These two Congregations, as well as several others which it is not necessary to enumerate, still exist, their functions being somewhat modified by the changing circumstances of the age. Their action is for the most part confined to matters of discipline, but they sometimes have questions of doctrine and moral obligation referred to them by the Pope, from whom, of course, they derive all authority that they possess.

I do not here undertake to show the advantage and utility of these Congregations, or of any other institutions connected with the discipline of the Catholic Church. From the remarks I have just previously made, it will be understood that I take all this for granted, and that I feel justified in doing so. Those who differ from me will, I trust, excuse me when they find that this conviction on my part does not interfere with the impartial fairness of my narrative.

Galileo, whom I believe to have been a devout Catholic, would, if he were here to speak for himself, agree with me in principle, however he might complain of the action of the Roman Congregations in his own individual case.

We shall then, as we proceed, inquire whether this celebrated philosopher was, as some imagine, a hero and a martyr of science, or, as others think, a rash innovator, who happened by chance to be right, but who had little or nothing but vain and foolish arguments to adduce in support of his doctrines. Perhaps we shall find that such critics, on either side, are but imperfectly acquainted with the facts of the case.