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celestial, or in other words to astronomy. The problems which it should consider, and the manner in which they ought to be solved, are treated of at some length; but even with respect to astronomy much which it is proposed to do is left undone, the whole tract being merely a fragment.
Bacon has nowhere else spoken so largely of astronomy; the ! eason of which apparently is, that he was writing just after Galileo's discoveries had been made known in the Sydereus Nuncius, published in 1611; a circumstance which makes the Descriptio Globi Intellectualis one of the most interesting of his minor writings. The oracles of his mind were in this case evoked by the contemplation, not of old errors, but of new truths.
The Thema Cæli, which contains a provisional statement of his own astronomical opinions, is immediately connected with the astronomical part of the Descriptio Globi Intellectualis. They are clearly of the same date, and form in reality but one work.
In the De Augmentis Bacon has expressed the same general views on the subject of astronomy as in these tracts; and they are in truth views which it was natural for a man not well versed in the phenomena of the science to entertain and to promulgate. What had been done by the old astronomers seemed to him full of useless subtleties and merely mathematical conceptions; men therefore were to be exhorted to cast all these aside, and to study the phenomena of the heavens independently of arbitrary hypotheses. Let us first obtain an accurate knowledge of the phenomena, and then begin to search out their real causes. Orbs, eccentrics, and epicycles must not stand between the astronomer and the facts with which he has to deal. In this language, which had been held by others, there is something not wholly untrue; yet the counsel which it contains would, if it could have been followed, have put an end to the progress of astronomical science. Let us obtain an accurate knowledge of the phenomena — this no doubt is necessary, but then how is it to be done? To say that instead of trying to resolve the motion of the planets into a combination of elementary circular motions, we ought to be content to save the appearances by means of spirals, is to no purpose unless we are prepared to give an accurate definition of the kind of spiral we mcan. Failing this, a statement that the
apparent path of a planet is a spiral or irregular line along which it moves with varying velocity, is much too vague to be of any scientific value whatever; and if we seek to give precision to this statement, we find ourselves led back again into the region of mathematical conceptions, or, if the phrase be preferred, of mathematical hypotheses. The distinction between what is real and what is only apparent lies at the root of all astronomy; and it is in vain to seek for a physical cause of that which has only a phenomenal existence, as for instance of the stations and regressions of the planets. Thus in two points of view, astronomy must of necessity employ mathematical hypotheses, firstly in order to the distinct conception of the phenomena, and secondly in order to be able to state the problems which w higher science is afterwards to solve. If the hypotheses employed are inappropriate, as in the systems of Ptolemy or Tycho Brahe, they may nevertheless have done good service in making it possible to conceive the phenomena, and moreover may serve to suggest the truer views by which they are to be replaced. Almost any hypothesis is better than none, “citius enim,” as Bacon has elsewhere said, “ emergit veritas ex errore quam ex confusione.” The wrong hypotheses doubtless lead to premature speculation touching physical causes; but this is a mischief which in course of time tends to correct itself, as we see in the Ptolemaic system, of which the overthrow was in good measure due to the cumbrous machinery of solid crbs which had been constructed to explain the motions mechanically. It came to be seen that even if this system could save the phenomena, it was unable to give a basis on which a just explanation of their causes could be founded.
I have said that almost any hypothesis is better than none. But the truth is that as soon as men begin to speculate at all an hypothesis of some kind or other is a matter of necessity. On merely historical grounds and apart from any consideration of the relation between facts and ideas, questions might be propounded to a writer who was trying to describe the phenomena of the heavens without introducing any portion of theory, to which he would not find it easy to give clear answers. Thus we know that one of the philosophers of antiquity affirmed that the sun is new every day ;-are you prepared, we might ask, to set aside the authority of Heraclitus, and to maintain your theory in opposition to his ? If you affirm that the sun which
set last night is the same as that which rose this morning, you are no longer a describer of phenomena, but, like those whom you condemn, a dealer in hypotheses.
However this difficulty is got over, you will at any rate not venture to confound Hesperus and the morning star. It is true that one of the great teachers of Greece long since asserted that they are the same; but the speculative fancies of Pythagoras must be rejected not less than those of Ptolemy or Regiomontanus.
We find that Bacon, both in the De Augmentis and in the following tract, speaks of the constructions of astronomy as purely hypothetical. In this he agrees with many other writers. It was a common opinion that these constructions had no foundation in reality, but were merely employed as the basis of mathematical calculations. They served to represent the phenomena, and that was all. This view, which has not been without influence on the history of astronomy, inasmuch as it made the transition from one hypothesis to another more easy than it would have been if either had been stated as of absolute truth, connected itself with a circumstance not unfrequently overlooked. The struggle between the peripatetic philosophers and the followers of Copernicus has caused an earlier struggle of the same kind to be forgotten. The Ptolemaic system is in reality not much more in accordance with the philosophy of Aristotle than the Copernican; and therefore, while the authority of Aristotle was unshaken, it could only be accepted, if accepted at all, as a means of representing the phenomena. The motions of the several orbs of heaven must, if our astronomy is to accord with Aristotle, be absolutely simple and concentric. On these conditions only can the incorruptibility of the heavens be secured. Consequently eccentrics and epicycles must be altogether rejected; and as the Ptolemaic system necessarily employs them, it follows that this system is only of value as a convenient way of expressing the result of observation. Such was the view of those who, while they adopted Aristotle's principles, were aware that the astronomical system with which he was satisfied, and of which he has given an account in the twelfth book of the Metaphysics, was wholly inadequate as a representation of the phencmena. But his more strenuous adherents went further, and followed Averroes in speaking with much contempt of Ptolemy and of his
system; an excess of zeal which Melancthon, in the spirit of conciliation which belongs to his gentle nature, has quietly condemned.'
Out of this antinomy, if the word may be so used, sprang several attempts to replace the Ptolemaic system by a construction which should be in accordance both with the phenomena and with Aristotle. Of these the best known is the Homocentrica of Fracastorius. As the name implies, all the orbs have on this hypothesis the same centre, and of these homocentric orbs he employs seventy-seven. But a fatal objection to this and all similar attempts is that they can give no explanation of changes in apparent distance. Fracastorius tries to set aside this objection by asserting that although the distance of some of the heavenly bodies from the earth may seem to vary, yet it never does so in reality, the apparent variation being caused by the varying medium through which they are
Though this explanation is wholly unsatisfactory, the wish to get rid of eccentrics and epicycles was sufficiently strong to win for Fracastorius a much more favourable reception than his complex and imperfect hypothesis deserved. He was spoken of as a man who had succeeded in overcoming the divorce which had so long separated astronomy from philosophy.
Of the similar attempt made by D'Amico I know no more than what is mentioned by Spiriti in his Scrittori Cozentini.
The Ptolemaic system being thus treated as a mere hypothesis by the followers of Aristotle, for of course the astronomers who accepted Purbach's theory of solid orbs must have regarded it as a reality, it was natural that Bacon should have thought that what we now call physical astronomy, that is the causal explanation of the phenomena, ought to be studied independently of this system. Whatever it had accomplished might be as well done without it. Spirals and dragons would be found sufficient to represent the phenomena, if the perverse love of simplicity which had led the mathematicians to confine themselves to circles and combinations of circles was once got rid of. Galileo's view of this matter is however un
I See Initia Physicæ.
? See Flaminius. (Carmin. lib. ii. f. 30. Ed. Lutet. per Nicol. Divilem.] It is remarkable that Delambre declares that he cannot see why Fracastorius should have thought his own system better than the old one. The reason is perfectly obvious if we consider the matter in connection with the history of philosophy.
doubtedly the true one, “ Le linee irregolari son quelle che, non avendo determinazion veruna sono infinite e casuali, e perciò indefinibili, nè di esse si può in conseguenza dimostrar proprietà alcuna, nè in somma saperne nulla ; sicchè il voler dire, il tale accidente accade mercè di una linea irregolare, è il medesimo che dire io non so perchè ei si accagia.")
Bacon was not the first who proposed to sweep away from astronomy the mathematical constructions by which it seeme! to be encumbered. We find in Lucretius nearly the same views as those of Bacon. The astronomers, Bacon often says, insist on explaining the retardation of the inferior orbs by giving them a proper motion of their own, opposite to that which they derive from the starry heaven: surely it would be simpler t) say that all the orbs move in the same direction with unequal velocities ; the inequality depending on their remoteness from the prime mover.
Compare with this the following lines of Lucretius:
“Quanto quæque magis sint terram sidera propter,
Tanto posse minus cum cæli turbine ferri :
But it was probably not from Lucretius that Bacon derived this way of considering the matter. For Tclesius, whom Bacon esteemed “the best of the novelists,” and whose pastoral philosophy, as he has not unhappily called it, was contented with vague speculations as to the causes of phenomena without any accurate knowledge of their details, had suggested to his followers that it was nowise necessary to resolve the motion of the sun into the motion of the starry heaven and the motion of his own orb, and that on the contrary this composition of motions is unintelligible. You may see, he affirms, with your own eyes the way in which the sun, moving with one motion only, advances continually from east to west, and alternately towards the north and south; all that is necessary is to admit that the poles on which he revolves are not constantly at the same dis