Precious Stones

The idea of stone and especially of precious stone is naturally fundamental to the rime petrose, which develop as their central motif the idea that the lady is a petra: as hard as a stone, but also as beautiful and as powerful as a precious stone. In Dante's time, precious stones are believed to have powers deriving from the star or planet that fashioned them. As one might expect, this power is thought of as radiating invisibly from them; it is hidden, but its propagation is nonetheless thought of on the model of light. Dante writes of the influence of the donnapetra as if it were a kind of light proceeding in a straight line toward him from her, against which he has no shield; often it is implicitly or explicitly identified with the lady's gaze. In "Così nel mio parlar" the metaphorics of light is exchanged for that of combat: the lady's glance is like an arrow or a spear from afar; in the course of the poem this combat at a distance turns into hand-to-hand combat and finally into the act of love, which culminates in a return to the exchange of glances, this time the

prolonged—and ultimately peaceful—mutual gaze of the lovers, finally reconciled, at least in fantasy.

As one would expect, the petrose give special prominence to the term petra. Petra is the only generic substantive for stone (or precious stone) used in the entire series; such generic terms as gemma, sasso, scoglio, roccia, speco, and grotta never appear. The third petrosa, "Amor, tu vedi ben," in which petra is used as a rhyme-word thirteen times, deploys the full range of Dante's use of the term. It is used generically in lines 11, 12, 18, 41, and 57, with metaphorical reference to the lady in line 62. It is used of a rock or stone (the normal word would be sasso ) in line 16, and of precious stones in lines 19 and 26, with metaphorical reference to the lady in lines 22 and 56. It is used of a specific precious stone, crystal, in line 26. In "Al poco giorno e al gran cerchio d'ombra" there is a similar range of usage: generic in lines 5, 9, 18, 26, and 34 (metaphorically of the lady in line 5), and of precious stone (metaphorically, again) in line 39.^[63] In "Io son venuto" and "Così nel mio parlar," the term petra, in rhyme with itself, is used for the very first mention of the lady—in "Io son venuto," as the concluding rhyme-word of the first stanza; in "Così nel mio parlar," in the second line of the poem, in a rime riche with the verb impetra ("acquires" or "turns to stone").

For the most part, the names of specific stones or precious stones are not used in the rime petrose. The exceptions are marmo in "Io son venuto," the adjective cristallina in "Amor, tu vedi ben," and diaspro in "Così nel mio parlar." Vital to the meaning of the second petrosa, "Al poco giorno e al gran cerchio d'ombra," is the specific meaning concealed in the last, apparently generic, use of the term. In each of the petrose, then, one kind of stone is specified either explicitly or by the context. As we shall see, the stones are significantly related in terms of opacity versus transparency: crystal permitting all to be seen, but jasper, marble, and the hidden stone opaque in differing ways. They are also related rhetorically, tropically: marmo and diaspro are the proper specific terms for what they name; in cristallina petra the substantive is generic, the specification adjectival; in "Al poco giorno" the specification is suppressed, and the generic term is troped (but occulte, in a hidden way) to refer to the specific one.

Moreover, Dante draws widely on the lore of precious stones (and of stones in general). In the Middle Ages occult or hidden powers were attributed to precious stones, as well as to a number of metals. These beliefs no doubt had their origin in popular superstition, but in the

thirteenth and fourteenth centuries they were shared by the educated; in fact they had received "scientific" explanation as a particular type of influence exerted by the heavenly bodies on sublunar substances. In other words, the "virtue" or hidden power of such a metal as gold was thought of as the concentrated power of the star, planet, or astronomical/astrological configuration that had brought it into being: in the case of gold, the sun.

In the universe as conceived by the more Aristotelian as well as the more Platonic thinkers of the high Middle Ages, the heavenly bodies governed all modes of change in the sublunar world, the realm of the elements and of things made out of them, including human bodies and temperaments.^[64] In the Commedia Dante was to assert that, other than the human soul, only three things had been directly created by God: the angels, the heavens, and first matter (Paradiso 29.25–36); the implication is that all else was brought into being by the heavens and their angelic movers.^[65] Aristotle had asserted (Meteorologica 3.4) that minerals—stones and metals—were formed from "exhalations" underground, which were then acted on by the force of the heavens. Aquinas's commentary on the passage explains:

Ita quod principium activum principale est virtus coelestis, quae dicitur virtus mineralis, a qua habent fossilia quaedam, puta lapides pretiosi, quandam virtutem coelestem et occultam: per quam occultas operationes vere exercent.
(Lectio 13 [Aquinas 1875 23:531])

Thus, because the heavenly bodies are the principal active principle, through a power of theirs known as the mineral-producing power, certain minerals, for instance precious stones, have a certain hidden power: through which they actually work hidden operations.

The supposed properties of precious stones were the subject of a large number of treatises of various lengths. The shorter and more typical form consists of a simple list of the properties of individual stones, often in alphabetical order. In many cases these go back to Pliny^[66] and Isidore of Seville's adaptation of him,^[67] as well as to treatises supposedly by Aristotle and Theophrastus; they exist in both prose and verse, in both Latin and vernacular versions.^[68] A particularly popular and widely read one, by the eleventh-century Marbodus, bishop of Rennes, discusses some two dozen precious stones in elegant and succinct Latin hexameters (PL 171; Riddle 1977).

The most famous literary account of the formation of precious stones is in Guido Guinizelli's canzone "Al cor gentil rempaira sempre amore";^[69] we may call it the simple Aristotelian theory:

          Foco d'amore in gentil cor s'aprende 
come vertute in petra preziosa, 
     che da la stella valor no i discende 
anti che '1 sol la faccia gentil cosa; 
          poi che n'ha tratto fòre 
per sua forza lo sol ciò che li è vile, 
stella li dà valore: 
così lo cor ch'è fatto da natura 
asletto, pur, gentile, 
donna a guisa di stella lo 'nnamora. 
               (11–20 [Contini 1960 2:463])

The fire of love is lit in a noble heart as is the virtue in a precious stone, for the power does not descend into it from its star until the sun makes it a noble thing; after the sun has drawn from it all that is base, its star gives it power: so a heart that nature has made elect, pure, noble: a lady, like the star, fills it with love.

Here three phases are distinguished in the production of the precious stone: the existence of a suitable material, the preparation of the material by the sun, and the descent of virtue into the stone from the star—which clearly implies the idea of the imposition of a substantial form on the prepared material.^[70]

The next stanzas further develop the analogy between lover and gem, distinguishing between the proud, who are like the mud (opaque to the rays of the sun and thus incapable of being prepared to receive the valore from the star), and the noble, who are like clear water (transparent and capable of form). A further stanza compares the lover, who takes his cues for action from the starlike lady, to the angels taking intention from the sight of God and turning their heavens according to it.^[71]

It was generally agreed that the light of the heavenly bodies, along with their motion and their changing positions, was the major principle of becoming in the sublunar realm. Even Aquinas asserted that the light of each of the heavenly bodies differed formally (i.e., substantially) from that of every other; he believed each to be unique in its species because intended to exert a distinct effect on the sublunar:

Si autem lux primo die facta, intelligitur lux corporalis, oportet dicere quod lux primo die fuit producta secundum communem lucis naturam;

quarto autem die attributa est luminibus determinata virtus ad determinatos effectus, secundum quod videmus alios effectus habere radium solis, et alios radium lunae, et sic de aliis.
(Summa theologica Ia, quaest. 70, art. 1 [Aquinas 1875 1:437])^[72]

For if the light made on the first day is understood to be corporeal light, we must say that on the first day light was produced according to the common nature of light; but that on the fourth day the heavenly bodies received specific powers ordered toward specific effects, as we see that the rays of the sun have effects different from those of the moon, and so on.

The simple or naive form of this doctrine has the inconvenience of making the earthly material entirely passive, attributing all imposition of form to the direct agency of the heavenly bodies (thus violating Aristotle's principle of indwelling causes).^[73] An extreme version is the following by the thirteenth-century Polish optical theorist Witelo, a follower of Albertus Magnus, in the dedication of his optical treatise to William of Moerbeck (Aquinas's associate and one of the most distinguished translators of the century):

Est enim lumen supremarum formarum corporalium diffusio per naturam corporalis formae materiis inferiorum corporum se applicans, et secum delatas formas divinorum et individualium artificum per medium divisibilem caducis corporibus imprimens, suique cum illis incorporatione novas semper formas specificas aut individuas producens, in quibus resultat per actum luminis divinum artificium tam motorum orbium quam moventium virtutum.
([Witelo] 1535 fol. 1)^[74]

For the light of the forms of the heavenly bodies is the diffusion through nature of the corporeal forms that apply themselves to the material of sublunar bodies, and, having brought down the forms of the divine individual makers into the mode of the divisible and imprinting them on bodies that pass away, through its incorporation with them it produces ever new specific or individual forms, in which we can see, because of the active light, the divine workmanship both of the heavenly spheres and of the intelligences that move them.

Witelo is thinking of the light of the stars and planets (especially, of course, that of the sun) as actually carrying down from above and imprinting on the elements the substantial forms they bear. Somehow the visible forms of things were transmitted by light through the air. Witelo is here expressing a view close to Robert Grosseteste's "metaphysics of

light"—by which he was influenced—a view that helps explain the intensity with which optics was studied in this period.^[75]

For many reasons, the most interesting medieval mineralogical treatise is the Mineralium liber by Albertus Magnus (1890–99 5:1–55),^[76] which has been translated and annotated by Dorothy Wyckoff (1967).^[77] As Bruno Nardi established, in both the Convivio and the Commedia Albert is a major influence on Dante's metaphysical and cosmological ideas;^[78] whether or not Dante knew the Mineralium liber, its positions are in most respects similar to those taken in others of Albert's works that Dante did know.^[79] Albert seeks to give an exhaustive philosophical-scientific account of the formation and virtues of stones, precious stones, engraved gems, and metals. After his general discussions, he includes alphabetically arranged lists that subsume most of the "information" contained in earlier lapidaries. Albert used a fairly wide variety of sources;^[80] he also adds comments of his own and refers frequently to his own experience.

All stones, Albert says, are formed from either earth or water: from earth by conglutinatio, from water by congelatio. Transparent stones are a kind of mean between earth and water, retaining qualities of each. Albert thinks of the four elements as embodiments of the basic qualities: hot, cold, wet, dry. The transformation of one element into another involves its gradual taking on of the other's properties. Thus if water is cold and wet, earth cold and dry, he finds it logical to think of stones as formed by water's gradually taking on the dryness of earth, which accounts for its solidity:

Cum enim terra ad se convertit aquam, primo virtutes terrae intrant substantiam, et alterant eam, et aquae quasi dominantes tenent eam: et tunc incipit aqua stare et terminari, et tamen adhuc perspicuitatem non omittit, et tunc deinde corrumpitur, et transit in terram, et accipit terrae qualitates, quae sunt opacum siccum.
(Albertus Magnus 1890–99 5: 12)

For when Earth converts Water into [Earth], first of all the power of Earth enters into the substance [of Water] and alters it, but that of Water, still dominant, contains it; then the Water begins to grow firm and be limited by a boundary, although as yet it does not lose its transparency; and then finally it is destroyed and passes into Earth, and takes on the qualities of Earth, opacity and dryness.
(Albertus Magnus 1967 33; translation revised)

Thus if the process is fixated while the material still retains the transparency of water, we have crystal and other transparent stones. The influence of external cold is thought of as a kind of pressure:

In montibus altissimis frigiditas est perpetua, quae est excellens . . . quae frigiditas exprimendo humidum apprehendit aquam a nivibus congelatam, et inducit in eam proprietates sicci, sicut est naturae frigiditatis excellentis: et ex illo sicco coagulat glaciem in crystallum vel alium lapidem perspicuum.
(1890–99 5:12; emphasis added)

In very high mountains there is perpetual and extreme cold . . . And this cold, by squeezing out the moisture, attacks the Water frozen by the snows, and induces in it the properties of dryness—for this is the nature of extreme cold—and then, out of that dryness, solidifies the ice into crystal or some other transparent stone.
(1967 32; translation slightly revised)

This is very close in conception to Seneca's description of the formation of crystal:

Aqua enim caelestis minimum in se terreni habens, cum induruit longioris frigoris pertinacia spissatur magis ac magis, donec omni aere excluso in se tota compressa est, et umor qui fuerat lapis effectus est.^[81]

For when water from heaven, that has very little of earth in it, has hardened through the persistence of long cold, it grows thicker and thicker, until, all the air having been expelled, it is entirely compressed into itself, and what was liquid has become a stone.

Seneca attributes the transparency of crystal to the purity of the air from which the water itself had been formed. Albert follows Aristotle's notion of transparency as a quality supremely possessed by the heavenly spheres:

Aliquando autem vis terrea apprehendit aquam ita quod frigidum iam exprimit humidum, et siccum terminat materia in seipsa, manente aquae transparentia. Pervietas enim aquae non convenit eidem in quantum est frigidum vel humidum vel utramque habens qualitatem, sed in quantum convenit cum coelesti corpore.
(1890–99 5:13)

Sometimes, too, an earthly force attacks Water in such a way that cold expels its moisture, and dryness causes it to take on the shape of a solid, although the transparency of the Water remains unchanged. For the

clearness of Water does not depend on how much it contains of the qualities of cold or moisture, or both, but upon how much it has in common with the substance of the heavens [Ether].
(1967 34)

Albert criticizes four theories of the production of stones in general: three of them are erroneous—(1) that they are formed by volcanic heat; (2) that they are produced by a soul of the stone; (3) that no substantial forms are produced—and the fourth is too general (1.1.4; 1890–99 5:6–7). The same pattern appears in his critique of the theories of the "virtues" of precious stones; three are erroneous—(1) that they derive from the elements that compose the stones; (2) that in them the supernal idea or form is less submerged in matter than in other objects; (3) that they are produced by the imaginings of the movers of the spheres (i.e., the angelic intelligences)—and the fourth is too general. The fourth, general cause in each case is the influence of the heavenly bodies.

On the powers of precious stones, Albert explains, "Hermes"^[82] and his followers believed

omnium inferiorum virtutes esse in stellis et imaginibus coelorum. Omnes autem virtutes infundi in inferioribus omnibus per circulum Alaur, quem primum circulum imaginum coelestium esse dicebant. Has autem virtutes descendere in res naturae nobiliter et ignobiliter. Nobiliter autem quando materiae recipientes has virtutes, fuerint superioribus imaginibus similes in lumine et perspicuitate. Ignobiliter autem, quando materiae fuerint confusae et foetulentae, in qua quasi opprimitur virtus coelestis. Haec igitur causam isti dicunt, quoniam lapides pretiosi prae aliis habent mirabiles virtutes: quia videlicet in substantia magis simulantur superioribus, et in lumine et perspicuitate: propter quod a quibusdam eorum stellae elementales esse dicuntur lapides pretiosi.
(Mineralium liber 2.1.2 [1890–99 5:26])

that all the powers of sublunar things are in the stars and constellations. For all powers are poured into sublunar things by the circle Alaur, which they said was the first circle of constellations, but they descend into natural things either nobly or basely: nobly when the materials that receive them are more similar to the heavenly bodies in brightness and transparency, basely when the materials are confused and muddy, in which the heavenly virtue is almost drowned. And this is the reason, they say, why precious stones have marvelous powers beyond other things, for they are in substance more like the heavenly bodies in brightness and trans-

parency, for which reason they are called by some "elemental stars" [i.e., stars made from the four elements, not from the "fifth essence"].
(our translation)

Except that it does not mention the phase in which the material is prepared, this theory is exactly the one implied by Guinizelli's analogy. Indeed, we have just seen that Albert attributes the transparency of certain stones precisely to their similarity to the heavens. He does not deny this theory, he regards it as too general:

hic non quaerimus causas agentes et moventes primas, quae forte sunt stellae et stellarum virtutes et dispositiones: hoc enim alterius scientiae proprium est: sed quaerimus causas efficientes proximas, quae in materia existentes materiam transmutant.
(Mineralium liber 1.1.4 [1890–99 5:6])

Here we are not inquiring into the first active and moving causes, which may be the stars and the virtues and positions of the stars, for this is the subject matter proper to another science; but we are inquiring into the proximate efficient causes that, existing in matter, transmute matter.

Albert's explanation is elaborate; the vis mineralis, he argues, comes into being only where the appropriate materials exist in a place naturally apt to produce minerals,^[83] and it functions in a way strictly analogous to that of the vis formativa in the father's seed as it shapes the embryo in the womb:^[84]

Dicimus igitur quod sicut in semine animalis quod est superfluum nutrimenti, descendit a vasis seminariis vis formativa animalis, quae format et efficit animal, et est in semine per modum illum quo artifex est in artificiato quod facit per artem: sic est etiam in materia aptata lapidibus virtus formans et efficiens lapides et producens ad formam lapidis hujus vel illius . . . cum materia sicci passi ab humido unctuoso, vel materia humidi passi, aptatur lapidi a sicco terrestri, et generatur in ipsa ex virtute stellarum et loci . . . virtus formativa lapidis, sicut generativa in semine a testiculis quando semen fluerit attractum ad vasa seminaria, et unaquaque materia secundum speciem propria virtus. Et hoc est quod dicit Plato, secundum merita materiae infunduntur virtutes caelestes.
(Mineralium liber 1.1.4 [1890–99 5:7])

We say, therefore, that as in the seed of an animal, which is superfluous food, there descends from the seminal vessels the animal formative power, which forms and fashions the animal, and which is in the seed in the mode by which the craftsman is in the object shaped by his craft: so also

in materials made suitable to be stones there is a power that forms and fashions the stones and produces them in the form of this or that particular stone . . . when there is dry matter that has undergone the action of oily moisture, or moist matter that has been acted on [by dry], and there is generated in it, out of the power of the stars and of the place . . . a power that forms stones, as the generative [power] descends into the seed from the testicles when it is attracted to the seminal vessels, and in each particular material its own power according to its species. And this is what Plato says: the celestial powers are infused according to the merit of the material.
(our translation)

Where there is suitable material in a suitable place, then, the stars infuse the vis mineralis, which operates purposefully (as an entelechy) through the hot and cold of the elements as through tools. It prepares the materials and imposes on them the substantial form of the stone. Albert insists that the vis mineralis is infused into the matter, operates within it, and eventually becomes the substantial form of the stone and thus, in the case of a precious stone, the source of its power (1890–99 5:11, 26).

Striking in Albert's theory is the projection onto the cosmic scale of the principles of sexual reproduction, the influence of the heavens being parallel to the pouring of seed into the womb of the earth. In essence, this is a version of the ancient myth of the hieròs gamós, the marriage of sky and earth. At another level it is interesting as an effort to devise a theory that will give a certain autonomy to earthly process, thought of as initiated by the first causes but proceeding in some sense on its own.^[85]

When he attempts to answer the question of why some places and not others are capable of producing minerals, Albert produces a clear statement of an analogy—very important for our understanding of the petrose —between the influence of the stars and the activity of human craftsmen:

. . . stellae qualitate et lumine et situ et motu movent et ordinant mundum secundum omnem materiam et locum generabilium et corruptibilium. Virtus autem sic determinata a stellis infunditur loco generationis unicuique rei, et modo quo in naturis locorum determinatum est. Haec enim virtus et elementi et elementati omnis est productiva et generativa.

Et est ista virtus loci ex tribus virtutibus congregata, quarum una est virtus motoris orbis moti. Secunda est virtus orbis moti cum omnibus

partibus suis et figuris partium quae resultant ex situ partium diversimodi se respicientium propter multimodam motorum velocitatem et tarditatem. Tertia autem est virtus elementaris. . . . Est autem prima harum virtutum ut forma dirigens et formans omne quod generatur, sicut virtus artis ad materiam artificiati se habet. Et secunda est sicut operatio manus. Et tertia sicut operatio instrumenti quod manu movetur et dirigitur ad finem inceptum ab artifice. Et ideo dixit Aristoteles quod omne opus naturae est opus intelligentiae. Locus enim recipit has virtutes, sicut matrix recipit virtutem formativam embrionis. Haec igitur virtus determinata ad lapidum generationem, in materia terrestri vel aquea est, in qua conveniunt omnia loca in quibus lapides generantur.
(1890–99 5: 11)

. . . the stars, by their [differences in] quality, light, position, and motion, move and order the world [by influencing] the matter and place of everything that can be generated or corrupted. The power of the stars, determined in this way, is poured into the place of the generation proper to each single thing, as has been explained in The Nature of Places. For this power generates and produces both the elements and elemented things.

The power of a place, then, is a combination of three [powers]. One of these is the power of the Mover that moves the sphere. The second is the power of the sphere that is moved, with all its parts, and the figures that result from the varying position of the parts with respect to each other as they move more rapidly or more slowly. The third is the power of the elements. . . . Now the first of these powers, since it is the form that shapes everything that is generated, is related to the matter of the thing made as is the virtue of art. And the second is related to it as is the operation of the hand. And the third corresponds to the operation of a tool that is moved by the hand and directed to the end conceived by the artisan. And therefore Aristotle said that every work of nature is a work of Intelligence: for the place receives these powers just as the womb receives the power that forms the embryo. This power, then, determined to the generation of stones, is in the earthy or watery materials which are common to all places where stones are generated.
(1967 29–30)^[86]

Albert was extremely fond of this analogy between human art and the operation of the heavens, and it occurs frequently in his works.^[87] Here the heavenly—angelic—intelligence (the "Mover") takes its idea from the eternal patterns of things in the mind of God, and through a power that is analogous to the virtus or habitus of art in human beings it directs the motion of the sphere, compared in its turn to the motion of the hand of a human artist. The elemental powers—the qualities hot, cold, dry, and wet—are like tools held by the hand because they act on the matter that is being shaped, as we have seen: "primo virtutes terrae

intrant substantiam [aquae]" (1890–99 5:12).^[88] The analogy between the heavenly bodies and the human craftsman necessarily involves the converse: that the process whereby the human artist shapes his material is like the shaping influence of the revolving heavens. As we have already suggested, this is one of the fundamental principles of Dante's new poetics. Also, the petrose ask what kind of causality can be exerted by human art—whether in the shaping of the artifact or through the shaped object itself.^[89]

The connection of human art with the causality of the heavens is more than just an analogy, for human intelligence and the capacity for artistic creation are themselves to some extent produced by the influence of the stars and planets in the horoscope of the individual; Dante unmistakably takes this view in his invocation of the stars of Gemini in Paradiso 22.^[90] Albert and Thomas both insist that human actions are not determined by the stars; still, the passage in which Aquinas discusses the indirect influence of the stars on the mind is very revealing:

Sciendum est tamen quod, licet corpora coelestia directe intelligentiae nostrae causae esse non possint, aliquid tamen ad hoc operantur indirecte. Licet enim intellectus non sit virtus corporea, tamen in nobis intellectus operatio compleri non potest sine operatione virtutum corporearum, quae sunt imaginatio, et vis memorativa, et cogitativa . . . ; et inde est quod, impeditis harum virtutum operationibus propter aliquam indispositionem corporis, impeditur operatio intellectus, sicut patet in phreneticis et lethargicis et aliis hujusmodi; et propter hoc etiam bonitas dispositionis corporis humani facit aptum ad bene intelligendum, in quantum ex hoc praedictae vires fortiores existunt; unde dicitur in secundo De anima, c. ix, quod "molles carne aptos mente videmus."

Dispositio autem corporis humani subiacet coelestibus virtutibus. . . . Ideo indirecte corpora coelestia ad bonitatem operantur; et sic, sicut medici possunt iudicare de bonitate intellectus ex corporis complexione, sicut ex dispositione proxima, ita astrologus ex motibus coelestibus sicut ex causa remota talis dispositionis. Et per hunc modum potest verificari quod Ptolomaeus in Centiloquio dicit: "Quum fuerit Mercurius in nativitate alicujus, in aliqua domorum Saturni, et ipse fortis in esse suo, dat bonitatem intelligentiae medullitus in rebus."
(Summa contra Gentiles 3.84 [Aquinas 1875 12:359]; see Nardi 1967a 71)

However, we should note that, though celestial bodies cannot be directly the causes of our understanding, they may do something indirectly in regard to it. For although the understanding is not a corporeal power, the operation of understanding cannot be accomplished in us without the operation of corporeal powers: that is, the imagination, the power of

memory, and the cogitative power. . . . And as a result, if the operations of these powers are blocked by some indisposition of the body, the operation of the intellect is impeded, as is evident in demented and sleeping persons, and in others similarly affected. And that is why even the good disposition of the human body makes one able to understand well, for, as a result of this, the aforesaid powers are in a stronger condition. Thus it is stated in De anima 2.9 that "we observe that men with soft flesh are well endowed mentally."

Now the condition of the human body is subject to the influence of the celestial motions. . . . So, the celestial bodies act indirectly on the good condition of understanding. Thus, just as physicians may judge the goodness of an intellect from the condition of its body, as from a proximate cause, so also an astrologer may judge from the celestial motions, as from a remote cause. And in this way can come true what Ptolemy wrote in the Centiloquium, "When Mercury is in the nativity of some one, in a house of Saturn, and is strong in his being, he gives a goodness of intelligence that sees deeply into things."
(Aquinas 1956 2:17–18; translation altered)

Dante states this doctrine explicitly in Book 4, chapter 2, of the Convivio:

Lo tempo, secondo che dice Aristotile nel quarto de la Fisica, è "numero di movimento secondo prima e poi"; e "numero di movimento celestiale," lo quale dispone le cose di qua giù diversamente a ricevere alcuna informazione. Ché altrimenti è disposta la terra nel principio de la primavera a ricevere in sé la informazione de l'erbe e de li fiori, e altrimenti lo verno; e altrimenti è disposta una stagione a ricevere lo seme che un'altra; e così la nostra mente, in quanto ella è fondata sopra la complessione del corpo, che a seguitare la circulazione del cielo altrimenti è disposta a un tempo e altrimenti a un altro.^[91]

One of the most curious parts of Albertus Magnus's treatise on minerals is his discussion of the powers possessed by precious stones engraved with images (sigilla )—usually, in his notion, astrological images,^[92] such as representations of constellations (we have seen him use the term figura for constellations, and there is no question that he thinks of them as a kind of picture outlined by the stars). He believes that the stars themselves sometimes imprint such images on stones and discusses the phenomenon at length, deciding that it is simply a special case of the imposition of form by the influence of the heavens.

Albert's explanation of the fact (as he regards it) that stones engraved by men have occult powers is most interesting. The typical case is a seal representing a constellation: it must be carved at the time the constel-

lation is in force, and usually it will possess virtue only when the astrological situation of its carving is repeated.^[93] Both in the intention of the carver and in the form he imposes on the stone, the constellation is the cause of the image, and it naturally will exert its influence through the human agency (carving) most fully when it is astrologically in power. The philosophical basis for this astounding notion is the doctrine of the transitivity of causal relations:

Non autem dubitandum, quin omne quod est causa aliquo modo causae, est etiam aliquo modo causa causati. Si igitur vis et afflatus siderum influit quandam causalitatem artis in artifice, pro certo nisi impediatur, influet omnibus operibus artis aliquid suae virtutis.
(Albertus Magnus 1890–99 5:51)

And it is not to be doubted that everything that is somehow the cause of a thing is also somehow the cause of whatever results. If, then, the force and inspiration of the stars pour some influence causing art into the artisan, certainly, unless it is somehow prevented, it will pour something of its power into all the works of the art.
(Albertus Magnus 1967 135; translation revised)

Albertus, Aquinas, and Dante all agree that, to the extent that artistic creation draws on fantasy, memory, and the power of association (vis cogitativa ), the three bodily faculties listed by Aquinas, it is affected by the influence of the heavenly bodies. The influence of the heavens, moreover, does not end at birth; it extends not only to the artist's basic complexion or constitution, but also to the daily, weekly, and seasonal variations of his bodily state as affected by the heavens.

As we shall see, these astrological doctrines of the influence of the heavens in shaping sublunar things, of the transitivity of heavenly causality through such privileged objects as precious stones, of the direct influence, both at birth and from day to day, of the heavens on the human temperament (including faculties directly involved in all artistic creation), and of the analogy between the influence of the heavens and the shaping activities of human craftsmen are all reflected in the rime petrose. In fact, it is not going too far to say that the petrose cannot be understood without taking these doctrines into account.