by Martin Kemp
The literary dimension resides in Leonardo’s fervent desire for his art to surpass poetry. In a paragone (comparison of the arts) that he wrote, Leonardo argued that sight, which operated though the prime human sense, conveyed images with a vividness and emotional power that poetry could not match.
“The portrait evolved into a ‘universal picture’ in which Leonardo invested his highest intellectual, imaginative, and technical skills.”
In the Mona Lisa, he implicitly challenged the poets’ evocation of the “beloved lady,” a central genre in Renaissance poetry. Dante (c. 1265–1321), whose poetry Leonardo knew well, spoke of the overwhelming power of the lady’s eyes and smiling lips. This became a standard trope in subsequent love poetry and featured in the poems that were written about Leonardo’s portraits of ladies. The image of Lisa as a smiling woman who looks at us but somehow remains enigmatic and out of reach translates the poet’s formulas into a living, visual presence. This presence is readily apparent in a digitally restored version, opposite, by optical engineer Pascal Cotte, which used algorithms to restore something of the original colors and allows us to gain a better sense of the space within the painting.
The scientific dimensions directly involve the optical phenomena to which Leonardo paid such attention, including the gradations of light and shade on solid bodies (see pages 76 and 79). More unexpected is the geological content. The landscape behind the sitter speaks of the past history of the body of the earth and tells us of events to come. We see the two high lakes of which Leonardo spoke in his analysis of the Arno Valley (see page 125). The upper lake will eventually burst through, and the dry riverbed to the left will be charged with seething waters. The artist was not literally portraying the prehistoric or future Arno, but was shaping Lisa’s landscape on the basis of what he had learned about change in the “body of the earth,” to stand alongside the implicit transformations in the body of the woman as a “lesser world” or microcosm.
Portrait of Lisa del Giocondo, 2010, digitally restored by Pascal Cotte.
69. Studies of the Optics of the Human Eye, with an Experimental Model of the Eye
c. 1507, Bibliothèque de Institut de France, E 3v
In his earliest studies of vision, Leonardo thought that sight was a simple business. A pyramid of light rays emanating from an object enters the eye to register its relative size and its distance. As he became more aware of medieval optical theory and gained more direct access to the sophisticated ideas of the Arabic philosopher Ibn al-Haytham (Alhazen, c. 965–c. 1040), Leonardo came to realize that the act of seeing was a complex process.
On this page from his manuscript On the Eye, we see the rays passing through the pupil, where they are inverted as in a camera obscura (a pinhole camera). The spherical crystalline humor reinverts the image, passing it to the optic nerve at the rear of the eye. (There was no sense at this time that the “crystalline humor” was stretched by muscles into a lens shape in order to focus images on the retina.)
In the manuscript, Leonardo worked through possible variations on the path of the rays. In this drawing here, toward the center of the page, he experimented with a system in which the second inversion occurs behind the crystalline humor. The smaller resulting pyramid then coincides neatly with the optic nerve.
He realized that simply drawing the possible paths of rays would not settle the matter. In the drawing at the top right, he devised an innovatory experiment to see what actually happens inside the eye. A large model of the eye was constructed with a pupil at its base and a sphere suspended in water in a glass bowl. The experimenter looked into the model eye through the rim of the glass bowl, with his own eye in the position of the optic nerve.
Leonardo was now aware that a receptive surface at the back of the eye will receive rays from various points on an object. The rays that pass through most directly will register the shape and position of an object most clearly, but not definitively—thus even close edges would appear blurred to some extent; the contours, nonlinear. Leonardo wrote that “the eye does not know the edge of any body.” This optical uncertainty is very apparent in his paintings from the Mona Lisa onward.
70. Study of the Vessels of the Arm, with a Demonstration of the Vessels of an Old and Young Person
c, 1508–10, Windsor, Royal Library, 19027r
This page of vascular studies is one of many that derived from Leonardo’s dissection of a man who had died in the Hospital of Santa Maria Nuova in the winter of 1507–8. The man, who claimed to be a hundred years old, faded away in front of Leonardo, who “made an anatomy to see the cause of a death so sweet.” He concentrated on the man’s vascular system, because it seemed his body was no longer adequately nourished by his blood vessels and that his organs and skin had become “desiccated.”
The larger drawing shows the main superficial vessels of the arm, mapped out as if Leonardo were looking at a river system. He was a staunch advocate of the ancient idea of the microcosm, in which the human body mirrored on a small scale the features of the earth and the wider system of the cosmos. He claimed that the bones are like the mountains, the soil is the flesh, and the vessels are the rivers, which he called the vene d’acque (veins of water). Leonardo gave the standard doctrine of the microcosm a new visual cogency and was able to use it as a research tool.
He decided that the old man’s vessels had become tortuous “in the manner of a snake,” and had silted up as a consequence. Leonardo knew from his hydraulic engineering studies that straight channels transmitted water with the greatest degree of efficiency, while meandering rivers left deposits as they curved back and forth. In the smaller drawings he illustrates vessels that are “young” and those that are “old.” The former pursue straight courses such that the blood can course through at full pace, whereas the latter would pass blood only in a sluggish manner. He noted that the vessel surrounding the heart of the centenarian was notably affected by silt, and diagnosed the cause of death as “weakness through failure of blood and of the artery which feeds the heart and lower members.”
71. Demonstration of the Vessels of the Thorax, and the Heart as the “Seed” of the Vascular System
c. 1508–10, Windsor, Royal Library, 19028r
Leonardo’s vision that the functioning of the human body was as at one with the operation of all natural systems reached its fruitful climax at the time of his dissection of the “centenarian.”
The heart serves as the “lake of blood” from which “the vessels originate, which make ramifications throughout the human body, similarly the Oceanic sea fills the body of the earth with infinite veins of water.” The rule of the microcosm extends to all living things. Analogies are everywhere. The way a tree branches exhibits a fundamental affinity with the branching of blood vessels.
So powerful is an argument based on analogy that Leonardo used one to solve a long-running physiological dispute about whether the heart or the liver is the source of the vascular system. Aristotle argued for the primacy of the heart, having studied embryo chicks, but Galen, the second-century Greek physician and philosopher, later maintained that the liver produced the blood, which was then distributed by the heart.
On this page, Leonardo began with the highly organized demonstration of the main vessels of the torso and upper abdomen, with just an outline to denote the position of the heart. He paid particular attention to the ramifications of the hepatic vessels, sensing that they are like roots. He then argued (in the note below the drawing) that “if you should say that the vessels arise in . . . the liver . . . just as the roots of the plants arise from the earth, the reply to this analogy is that plants do not have their origin in their roots. . . . This is seen through experience in the germination of a peach that originates from its stone.”
The diagrammatic images in the upper left show the heart (core) with the main vessels, and a fruit stone (nocciolo). It is readily evident that “the tree of the vessels . . . has its roots in the manure, that is to say the mesenteric veins [that feed and
drain the intestines] go on to deposit the blood they have acquired in the liver.” Thus, “the heart is the nut that generates the tree of the vessels.”
72. Demonstrations of the Trachea and the Branching of the Bronchi in the Lungs and the Organs of the Upper Abdomen
c. 1508–10, Windsor, Royal Library, 19054v
This is one of the most beautiful and cogent of Leonardo’s synthesized demonstrations of the systems of the body. It combines organic form with his characteristic search for the mathematics of structure and function. It is one of a series of studies that concentrates on the irrigation channels that conduct fluids around the body.
The note beside the lateral view on the right shows four conduits and the spine: “a trachea, whence the voice passes/ b esophagus, whence the food passes/ c apoplectic vessels [the pair of carotid arteries] whence passes the vital spirits/ d dorsal spine where the ribs arise/ e vertebrae, where the muscles arise that terminate in the neck and raise the face to the sky.”
Leonardo’s focus in the highly developed demonstration on the left is on the way that the trachea bifurcates regularly. He thought about how the complex spatial array might be displayed most comprehensively and lucidly: “first make this lung complete, seen from four aspects in its complete perfection; then you will make it so it is seen fenestrated, solely with the ramifications of the trachea from four other aspects.” As in his illustrations of the Platonic solids (see page 80), “fenestrated” means rendered in a skeletal mode in space without any intervening material.
We know from his analysis of branching in trees that the total cross-sectional area of the branches at any level in the system should remain constant. Thus the cross section of each of the two conduits at the first stage of branching should be a half of the main one, the next would be a quarter, and so on, proportionately. If this rule of equality is broken, the flow will be disrupted. Leonardo knew that this rule applied to all systems that transport fluids in the human body and in nature more generally. In modern terms, he was showing that the volume of a fluid passed at constant velocity is proportional to the cross-sectional area of the channel.
73. Demonstration of the Irrigation Systems of a Female Body
c. 1508–10, Windsor, Royal Library, 12281r
The culmination of Leonardo’s campaign to chart the irrigation of the human body is this very large study of plural systems within the outlines of a woman’s body. He valiantly attempted to unite the vascular, respiratory, urinary, and reproductive systems, using his innovatory techniques of representation.
The arteries and veins branch systematically into progressively smaller tributaries, as do the bronchial tubes. The heart appears to consist of two chambers, an interpretation that Leonardo was to abandon shortly after making this drawing. The spherical womb is a traditional feature, with its lateral “horns.” Throughout, the artist was combining morphological knowledge gained from dissections with his conception of how the components function in the context of traditional physiology. His ultimate aspiration in anatomy was to “remake” the human body as a functional machine rather than to provide “descriptive anatomy” in the manner of Henry Gray’s famous textbook in the nineteenth century.
He deployed a remarkable range of graphic techniques in the one drawing, using ink and black chalk. Some forms are shown as solid, some are in shadow, some are sectioned, and others are rendered as if transparent. His ambition was to create an ultimate composite of the bodily systems. Undaunted, he reminded himself on the left of the drawing to “make this demonstration also as seen from the side . . . and then make one from behind.”
The main outlines are pricked for transfer to another sheet, presumably so he could clarify those parts where the overlaid features had become confusing. We may imagine that he had made or was intending to make three comparable demonstrations of the male body, as well as of the woman from the side and back.
The note on the left contains an obscure meditation on life and death: “Man dies and is always reborn in part by the mesenteric vessels, which are the root of vital nourishment. . . . One takes up life and the other gives out death. . . . This process is the ultimate one that only occurs in underground, that is to say in graves.”
74. Studies of a Wig for Leda
c. 1506–15, Windsor, Royal Library, 12516
Leonardo’s Leda and the Swan—his only painting of a mythological subject—was regarded as one of his greatest paintings and was very influential. There is no record of it after 1775. It is now known through a series of copies and variants, of which that at Wilton House (below right) is probably the best. It shows Leda, the Queen of Sparta, in close company with the swan who seduced her (Jupiter in one of his many rapacious disguises). The four progeny of their union surge boisterously from two giant eggs. The setting is moist and succulent. It was very much an essay on the fecundity of nature.
Other ancient and Renaissance representations of this subject depict the act of intercourse. Leonardo’s depiction was conceived not as a narrative but as a sensual portrayal of the naked Leda with her attributes—the swan and the babies.
A series of very spirited drawings survives, including early ones in which Leda kneels in a twisting pose based on a Roman Venus. The studies on this sheet (opposite) in pen and ink with black chalk are for Leda’s very elaborate wig. They feature the insistently curved pen strokes that Leonardo increasingly adopted after 1500.
The intricate plaits and whorls of the wig itself work tightly engineered variations on the vortex motion of water. Leonardo noted that “the motion of the surface of water . . . resembles the behavior of hair” (see full quote on page 183). He made play between the artificial vortices of the wigmaker’s art and the licentious freedom of Leda’s own hair, which cascades from the lateral edges of the wig and spouts forth from the center of the whorls.
Typically for Leonardo, he was not content to invent something that would work only in the picture—he also had to understand the total structure of the wig. Thus we see two variants of the back, the lower of which displays a developed knot design. Beside a study of the wig on another sheet he wrote, “this can be taken off and put on without damaging it.”
Leda and the Swan, after Leonardo, unknown artist, c. 1525.
75. Studies of the Star-of-Bethlehem (Ornithogalum umbellatum), Crowfoot (Ranunculus aquatilis), Wood Anemone (Anemone nemorosa), and Sun Spurge (Euphorbia helioscopia)
c. 1506–8, Windsor, Royal Library, 12424
Along with his many other projects for treatises on aspects of nature, Leonardo was considering a “discourse on herbs.” Both the star and the sun spurge were medicinal herbs (both are now considered unsafe to consume). To this end, he began recording the appearances of various plants and their flowers as a guide to their identification, and as a hymn to nature’s inventive beauty. However, as in all his studies of nature, he sought to draw out the structural rationales of the whole and parts.
The main plant on this page, the star-of-Bethlehem, is drawn with wonderful rhythmic vitality. The stems of the star-like flower sprout above thin leaves that surge from the center of the plant like water in vortex motion. The basic disposition of the plant is accurate, but the leaves have been organized by Leonardo in a way that is very improbable in a natural specimen. He constructed an ideal specimen that speaks in a very definite way of spiral growth. It is what he called a “demonstration.”
The close presence of the plants to the left and right seem to suggest that he was looking at flowers in a meadow, but it is equally likely that he was creating a composition from picked flowers with accompanying leaves.
He was particularly fascinated by the unusual structure of the inflorescences and branches of the succulent sun spurge on the bottom right. While looking at plants, he always had in mind structural features that might let him devise a classification. On a drawing of a rush and sedge he attempted to define the “types” of rushes, and noted that one had a round stem while another was triangular in cross section.
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br /> The portrayal of the plants on this sheet is fully in keeping with the vegetation he was planning for his Leda and the Swan (see page 141). On the fertile ground, plants, including bulrushes, were to be growing in lush abundance. These component parts of living nature belonged to the same system of “vivification” in the “body of the earth.”
76. Studies of Turbulent Flow Past Tilted Obstacles and Water Falling into a Pool
c. 1508–9, Windsor, Royal Library, 12660v
This astonishing drawing stands at the climax of Leonardo’s intense studies of water in motion, including those in the Codex Leicester (see pages 146–47). The setup in the main study resembles that of the experimental tank with glass sides that is twice illustrated in the Codex. The skeins of vortices streaming out behind the rectangular obstacles in the two upper drawings irresistibly resemble flowing hair. Leonardo noted more than once this analogy between water and hair (see pages 141 and 183), adding that “the motions of wind resemble those of water.”
The main study may be regarded as a composite “anatomy” of turbulence, compiled in much the same manner as the great synthesis of the anatomy of a woman on page 138. It brings together various hydrodynamic components: the motion of water “in itself” inexorably completing its whirling action according to the amount of impetus embedded in each current; the rebounds of water striking water at the point of the water’s entry into the pool, where the surface is forced downward; rebounds from the bottom of the pool; and the rise of submerged bubbles that surge upward in rosette formation, exploding noisily at the surface.
Leonardo himself aspired to classify the effects: “the motions . . . are of three kinds, to which a fourth may be added, which is that of the air being submerged in the water.” He somewhat lost track of his classification during the course of his heroic efforts to cope with the variables involved. For instance, “this water then emerges in the shape of large bubbles, acquiring weight in the air and on this account falls back through the surface of the water, penetrating as far as the bottom, and it percusses and consumes the bottom.”