not admit of any determination either in the category of quantity or any other. Whatever may be thought of the value of the Aristotelian antithesis of form and matter, we are not at liberty to charge it with difficulties which only arise when we forget that, in this antithesis, matter does not mean any actually existing thing. We must not replace the merely negative notion of the Aristotelian λn by the positive idea of substance, and then interpret the dictum that matter is indifferently susceptible of all forms, so as to make it mean that the quantity of a given portion of substance can be conceived to vary. That this transition from matter to substance has been often made, may readily be admitted; it is only one instance of the tendency of the mind to replace highly abstract notions by others which are less so, a tendency which, in the history of philosophy, is as the ódòs eis Tò Kúтw of Heraclitus.

66

In commending those who deny that primitive matter is quanto plane spoliata, licet ad alias formas æqua," Bacon refers to the Averroists, who ascribed to matter, considered apart from any form, extension in three dimensions-interminate extension, as it was usually expressed. Any attempt to give metes and bounds to this interminate extension would have been in the opinion of Averroes, as well as in that of the other followers of Aristotle, to introduce an sidos or form. This doctrine was however regarded by the orthodox schoolmen as little less of a heresy than that which Averroes had promulgated touching the soul of man. Another and a somewhat earlier doctrine ascribed to all matter a form of corporeity, prior to the introduction of any special or particular form. Both these doctrines are of Arab origin, the last-mentioned being that of Avicenna: they seem to spring from the same character of mind, though Avicenna's opinion is strongly condemned by Averroes. It does not seem to have ever been received with much assent, though the phrase "form of corporeity" became long afterwards famous, when Duns Scotus introduced it into his psychological theory.

Bacon is scarcely justified in asserting that Aristotle reduced the whole question of density and rarity to "the frigid distinction of act and power." He said, on the contrary, that density and rarity, instead of being, as at first they seem to be, purely qualitative conceptions, pass into another category than that of quality, when they are more narrowly examined. His

expressions are sufficiently remarkable to be quoted:- OUKE.. ἔοικε ἀλλότρια τὰ τοιαῦτα (namely the rare and the dense, the smooth and the rough) εἶναι τῆς περὶ τὸ ποιὸν διαιρέσεως· θέσιν γὰρ μαλλόν τινα φαίνεται τῶν μορίων ἑκάτερον δηλοῦν· πυκνὸν μὲν γὰρ τῷ τὰ μόρια σύνεγγυς εἶναι ἀλλήλοις, μανὸν δὲ τῷ διεστάναι ἀπ' ἀλλήλων, καὶ λεῖον μὲν τῷ ἐπ ̓ εὐθείας πὼς τὰ μόρια κεῖσθαι, τραχὺ δὲ τῷ τὸ μὲν ὑπερέχειν τὸ δὲ ἐλλείπειν. "The dense and the rare, the smooth and the rough, seem to be foreign from the classification of qualities. For each of them seems rather to denote a mode of disposition of the particles: the dense consists in their being near one another, and the rare in their standing apart; the smooth in their lying somehow in a straight line, and the rough in this- that one particle projects and another comes short.”

This explanation is precisely the same as Bacon's; and on the other hand Aristotle would have adopted Bacon's caveat "Neque propterea res deducitur ad atomum, qui præsupponit vacuum et materiam non fluxam (quorum utrunque falsum est), sed ad particulas veras quales inveniuntur."1

In this as in some other instances, Bacon speaks of Aristotle with needless disrespect. Yet even now Aristotle has not lost his claim to be accounted "il maestro di coloro che sanno."

One of the applications which Bacon makes of his table of specific gravities is to the common doctrine of the elements, to which he esteems it a fatal objection, that many bodies, as gold for instance, are much heavier than the densest of the elements. The objection would be conclusive if it were more difficult to believe that any mixture of the elements could by condensation become of the same specific gravity as gold, than to believe that it could possess the qualities by which gold is distinguished from other substances.

From comparing the densities of tangible bodies "quæ pondere dotantur," Bacon proceeds to speak of aeriform or pneumatical bodies, whose density cannot be judged of by their weight. In classifying aeriform bodies, he distinguishes, as in the Historia Vitæ et Mortis, between the crude spirits which are present in every tangible substance, and the animal spirits which are peculiar to living creatures. The latter are much the rarer, and possess positive levity; which appears in

1 Nov. Org. ii. 6.

238

PREFACE TO THE HIST. DENSI ET RARI.

the difference of weight of the same animal before and after death. Between these two kinds of spirits stands, in the scale of rarity, the ambient air, which is devoid of levity; a bladder filled with air not being lighter than when empty. It is scarcely necessary to remark that this observation proves nothing. Whether the air was in its own nature light or heavy, a portion of it separated from the rest by being enclosed either in a bladder or in any other envelope would clearly not tend either upwards or downwards. The principle of sufficient reason seems enough to show that any given portion of air must, in relation to the general mass, remain at rest. It is on this account that [J. B. Benedetti], of whom M. Libri gives an account, greatly condemns Aristotle for not having perceived that in its own place air has no weight.'

In order to connect the density of tangible bodies with that of air, Bacon tried to ascertain what quantity of spirits of wine would, when converted into vapour, completely fill a bladder of a known size. His result is, that the vapour occupied more than three hundred and twenty times as much space as the spirits themselves.

The remainder of the Historia Densi et Rari consists of a miscellaneous collection of remarks on dilatations and condensations, and on the different causes by which these changes are brought about. There is not much of interest in this part of the treatise. The whole concludes, like the Historia Vita et Mortis and the Historia Ventorum, with a number of Canones Mobiles, followed, as in the Historia Ventorum, by a list of things yet to be accomplished. The most remarkable circumstance connected with the Canones is the emphatic rejection of the doctrine of a vacuum. In this respect the Historia Densi

et Rari is completely in accordance with the Novum Organum, and both show that Bacon's opinions must have undergone a decided change after the time of his writing the Cogitationes de Rerum Naturâ, or the essay on the fable of Cupid.

1 Libri, Histoire des Sciences Mathém. liv. ii. p. 125.

NOTE.

DR. RAWLEY, whose copy of this treatise, as printed in the Opuscula, is our only authority for the text, does not tell us in what state he found the manuscript. I apprehend however that it came into his hands either unfinished or mutilated.

It was evidently meant to correspond in form with the two preceding tituli, namely the Historia Ventorum and the Historia Vitæ et Mortis, and to be set forth according to the plan described in the Norma historia præsentis, p. 17.; and had Bacon prepared it for the press himself, he would certainly not have omitted the Topica Particularia sive articuli inquisitionis. This, being a particular description of the order of inquiry, would have followed the aditus. Each section of the historia would have been assigned by a marginal reference to its proper article, would have been introduced by a connexio, and followed by observationes majores or commentationes; the monita and mandata being inserted in their places immediately after the paragraphs to which they had reference, and distinguished from the historia by italics or some other typographical difference.

Now in Dr. Rawley's edition we find no Topica Particularia; consequently no references to the several articuli inquisitionis to which the successive portions of the historia relate. In the earlier part of the inquiry, which treats de exporrectione materiæ in corporibus, secundum consistentias suas diversas, dum quiescunt, we find no connexiones, nor anything to indicate the particular relation which the several tabulæ, monita, mandata, observationes, commentationes, &c., bear to each other, or to the subject of inquiry. These are all printed in separate groups; each group having its separate heading (monita, mandata, &c., as the case may be); and the paragraphs into which they are divided are separately numbered; except towards the end, where the numbers are omitted. Thus the various monita which are dispersed through this part of the work are numbered from 1 to 6, after which occur three single ones without any numbers; the various observationes from 1 to 9, and afterwards one without any number; the mandata from 1 to 4; and so on. The paragraphs however to which the several series of numbers apply are not kept together, but intermingled. After the first tabula, for instance, we have monita 1, 2, 3, 4; then observationes

1, 2, 3; then mandata 1, 2; then observationes 4, 5, 6; then mandatum 3; then vellicationes de practicâ, 1, 2, 3, 4; then observatio 7; then historia 1; and so on. From all which I am inclined to suspect that the arrangement of this part had not been completed by Bacon; that Rawley found the monita, mandata, &c., set down in numbered paragraphs on separate sheets, and that the distribution of them into their places in the order of inquiry was his own work; a work which, without the help of the articuli inquisitionis, which should have given the directions, it would not have been easy to accomplish successfully, even if the materials had been themselves complete, which I can hardly think they were.

However that may be, the result is certainly not satisfactory. As the text stands, the relation which the several paragraphs bear to each other is far from clear, and the typographical arrangement (which differs materially from that adopted by Bacon in the two histories edited by himself) is perplexing from the absence of all distinction between the major and minor divisions; not always consistent with itself; and in some places positively incorrect. That it has not been reproduced in its original form by any subsequent editor, is not therefore a matter of regret; but the changes which have been introduced by modern editors (following, with some variations, the example of Blackbourne) do not appear to me to be exactly of the right kind; the object which they had in view being apparently to make the printed page neater and more compact, rather than to exhibit more clearly the order of inquiry and the divisions of subject.

My own object in arranging the text of this third titulus, has been to bring the typographical form more into symmetry with that of the two others. In them, it will be observed, the whole inquiry *is distributed into several articuli; each article having its separate connexio, which marks and explains the transition from the article preceding; its separate historia, with monita, mandata, &c., interspersed; and its separate observationes or commentationes (as the case may be), generally coming in at the end, and always distinguished (as stepping beyond the region of pure history into that of interpretation) by being printed in a larger type. That a similar logical arrangement was meant to be followed in the present history is evident enough even from the text as edited by Rawley. But in order to make this arrangement apparent to the eye, so far as that could be attempted without altering the words or the order of paragraphs, I have found it necessary to introduce some headings which are not in the original, and to alter the places of others. I have not however added anything except within brackets, nor altered or omitted anything without mentioning it in the notes. J. S.