What theory of the earth, then, did Leonardo seek to support with paleontological data? Simply stated, Leonardo was vigorously promoting a common and distinctively premodern view that could not have been more central to all his thought and art: the comparison, and causal union, of the earth as a macrocosm with the human body as a microcosm. We tend to regard such comparisons today as “merely” analogical or “purely” metaphorical—more apt to promote a deluding sense of false unity than any genuine insight about common causality. By contrast, Leonardo’s premodern world viewed such consonances as deeply meaningful, in part by invoking the same general theory of symbolic correspondence across scales of size and realms of matter that Leonardo (ironically) had rejected so vigorously in denying the Neoplatonic idea that fossils might grow within rocks as products of the mineral kingdom.
No theme recurs so incessantly, and with such central import, both in the Leicester Codex and throughout Leonardo’s writing, as the causal and material unity of the body’s microcosm and the earth’s macrocosm. Leonardo also knew the ancient pedigree of this doctrine, from classical antiquity through medieval Scholasticism. In the A Manuscript (now in the Institut de France), Leonardo stated that he would begin his “Treatise on Water” (never completed or published) with a statement that he later repeats almost verbatim in the Leicester Codex:
Man has been called by the ancients a lesser world, and indeed the term is rightly applied, seeing that if man is compounded of earth, water, air and fire, this body of the earth is the same; and as man has within himself bones as a stay and framework for the flesh, so the world has the rocks which are the supports of the earth; as man has within him a pool of blood wherein the lungs as he breathes expand and contract, so the body of the earth has its ocean, which also rises and falls every six hours with the breathing of the world [the tides]; as from the said pool of blood proceed the veins which spread their branches through the human body, in just the same manner the ocean fills the body of the earth with an infinite number of veins of water.
We need go no further than Leonardo’s most celebrated creation—the Mona Lisa—to recognize the analogy of macrocosm and microcosm as the centerpiece of his thought. La Gioconda stands on a balcony overlooking a complex geological background of flowing waters that complete a full hydrological cycle just as blood moves through the human body. Martin Kemp notes:
The processes of living nature are not only mirrored by anatomical implication within the lady’s body, but are more obviously echoed in the surface details of her figure and garments, which are animated by myriad motions of ripple and flow. The delicate cascades of her hair beautifully correspond to the movement of water, as Leonardo himself was delighted to observe: “Note the motion of the surface of the water which conforms to that of the hair.” . . . The little rivulets of drapery falling from her gathered neckline underscore this analogy, as do the spiral folds of the veil across her left breast.
We now reach the central dilemma that makes the paleontological observations so crucial to the argument of the Leicester Codex. This notebook, as scholars have always recognized, is primarily a treatise on the nature of water in all its properties, manifestations, and uses. Why, then, does Leonardo devote so much apparently subsidiary space to the nature of fossils and the reason for their situation in mountain strata, far above present sea level? The key to this problem lies in his almost heroic struggle to overcome a central difficulty in validating his crucial analogy of the body’s microcosm to the earth’s macrocosm. Most scholars have missed this theme, and therefore do not grasp the union of the hydrological and paleontological passages of the Leicester Codex.
Leonardo recognizes only too well—for he has struggled with this problem for years, and through several notebooks—that his crucial analogy suffers from a potentially fatal difference between the human body and the earth. Both are constructed from the four elements of antiquity: earth, water, air, and fire. But the human body sustains itself by circulating these elements, particularly by maintaining some mechanism for permitting water (blood) to rise from the legs to the head. The analogy of microcosm and macrocosm can only work if the earth also possesses a comparable device for sustenance by cycling.
But how can such a notion be defended for the planet, especially in the face of an apparently disabling problem: earth and water are heavy elements; their natural motion must produce a downward flow (leading ideally to a planet of four concentric layers with earth at the center, water above, air atop water, and fire at the periphery). If earth and water must move down, these heavy elements will eventually stabilize as two concentric spheres at the center of the planet—and the macrocosm will therefore possess no device for sustenance by circulation. Leonardo knows that he must therefore find a mechanism to make both earth and water move up (against their natural tendency), as well as down, on our planet. This pressing need, so difficult to validate, sets the central struggle that engages Leonardo throughout the Leicester Codex.
Ironically, I wish to argue, he never did solve his problem for the main subject of the codex—water. That is, he tried again and again, but never found a satisfactory mechanism to guarantee the upward motion, hence the cycling, of water. However—and we now come to the crucial point that has usually been missed—Leonardo did succeed (by his standards) in the quest to find a mechanism for upward movement of the other heavy element: earth. Fossils on mountains provide the observational proof that earth can rise, both generally and often, for marine shells once inhabited the sea but now reside in the high mountains. The paleontological observations form a centerpiece in the Leicester Codex not, as has usually been argued, because fossils once lived in water and the codex treats water in all major aspects (an awfully lame reason for devoting so much space to paleontology), but rather because fossils record Leonardo’s great success (in contrast to his failure for the central subject of water)—his key evidence for a general mechanism to drive the upward motion of earth, and therefore, his proof for a self-sustaining planet that may legitimately be compared with the human body.
Leonardo knew only too well that he faced a serious problem with the motion of water through the earth, and he virtually obsesses over the issue in notebook after notebook, repeating the conundrum in almost unchanging words, and proposing various solutions, only to abandon them later as untenable. Water, by itself and following its “natural course” (Leonardo’s words), can only flow down. But within the earth, water must also move up along internal channels (comparable with blood vessels of the human body) to emerge as springs in the high mountains (and thence, back on track, to flow as rivers to the sea). An earthly force must therefore make water rise through the land against its natural inclination to flow down. The combined action of these two forces will cause water to circulate—and thereby act like the blood in our bodies to sustain a living system.
So does the water which is moved from the deep sea up to the summits of the mountains, and through the burst veins [mountain springs] it falls down again to the shallows of the sea, and so rises again to the height where it burst through, and then returns in the same descent. Thus proceeding alternately upwards and downwards at times it obeys its own desire [to move down] at times that of the body in which it is pent [to move up]. (From the Arundal Codex in the British Museum.)
Leonardo could not have been more explicit in admitting that water can move upward only by running against its natural course and that, if any mechanism can be found at all for this anomalous motion, the analogy between microcosm and macrocosm offers the only reasonable hope:
Clearly it would seem that the whole surface of the oceans, when not affected by the tempest, is equally distant from the center of the earth, and that the tops of the mountains are as much farther removed from this center as they rise above the surface of the sea.3 Unless therefore the body of the earth resembled that of man it would not be possible that the water of the sea, being so much lower than the mountains, should have power in its nature to rise to the summit of the mount
ains. We must therefore believe that the same cause that keeps the blood at the top of a man’s head keeps water at the summit of the mountains. (From the A Manuscript in the Institut de France.)
But to state a need is not equivalent to finding a mechanism. Throughout the Leicester Codex, Leonardo struggles to discover a physically workable way to raise water within the earth. He tries and rejects several explanations, as Martin Kemp documents in an article entitled “The Body of the Earth.” Perhaps, Leonardo first argues, the heat of the sun draws water up through the veins (internal streams) that run through mountains. (Leonardo, in his strongest image of a living earth, had written in the Leicester Codex: “The body of the earth, like the bodies of animals, is interwoven with a network of veins, which are all joined together, and formed for the nutrition and vivification of the earth and of its creatures.”) But he then realizes that this explanation cannot work for two reasons—first, because, on the highest mountaintops closest to the heating sun, water remains cold, and even icy; and, second, because this mechanism should operate best in summer during maximal solar heat, but mountain rivers often run with lowest waters at this time.
In a second try, Leonardo turns to the earth’s internal heat and a process of distillation: perhaps the interior fires boil water in internal caverns, and this water rises as vapor through mountain interiors, where it reverts to liquid form and bursts through as a high spring. But this proposal won’t work either because such extensive distillation would require that the roofs of internal caverns be wet with the rising steam—but they are often bone-dry. Leonardo then made a feebler third attempt: perhaps, by analogy to a sponge, mountains somehow suck up water to a point of saturation and subsequent oozing from the top. But Leonardo realizes that he cannot cash out this analogy in mechanical terms:
If you should say that the earth’s action is like that of a sponge which, when part of it is placed in water, sucks up the water so that it passes up to the top of the sponge, the answer is that even if the water itself rises to the top of the sponge, it cannot then pour away any part of itself down from this top, unless it is squeezed by something else, whereas with the summits of the mountains one sees it is just the opposite, for there the water always flows away of its own accord without being squeezed by anything.
(One may wonder, of course, why Leonardo doesn’t invoke an explanation recognized in his day, and now known as “obviously” correct—that water “moves up” as evaporated vapor, later to fall as rain on mountaintops. In fact, Leonardo reluctantly acknowledged this resolution in notebooks written later than the Leicester Codex. But, when we get “inside” Leonardo’s head and his own explanatory world, we can easily see why he would shun a resolution that now seems so obvious to us. Leonardo wanted to prove that water in a living earth moves like blood in a living body—and this analogy required that water flow both up and down within earthly channels that could be likened to blood vessels. Blood does not evaporate and fall as rain in our heads!)
But if Leonardo, to his great disappointment, never solved the problem of rising waters, he did (to his satisfaction) crack the equally knotty problem of a general mechanism for the elevation of earth—a combination of his views on gravity and his concept of erosion. (I struggled with Leonardo’s complex mix of ideas for many days—a mélange of scholastic theories of gravity and the earth, mainly vouchsafed to Leonardo by Jean Buridan through the books of Albert of Saxony, and of Leonardo’s conjectures on composition of the earth’s interior combined with observations on our planet’s surface—but I am now confident that I grasp the argument and can present a crisp epitome.)
Our planet has a geometric center, called by Leonardo the “center of the world” or sometimes the “center of the universe”—for Leonardo predated Copernicus and accepted the Ptolemaic system of a central earth and a revolving sun. The realm of liquid water must arrange itself as a perfect sphere about this center, with the surface of the ocean equidistant at all points from the center of the world. If solid earth were homogeneous and equally distributed, this element would also form a smooth sphere with a surface equidistant at all points from the center of the world. (By the way, and contrary to popular mythology, all scholars recognized—and had known since antiquity—that the earth was spherical and not flat.)
But the heavy earth is far from homogeneous. The interior of our planet is a complexly marbled mass composed of solid earth, liquid water running through veins in the rocks, and even air, where water has hollowed out caverns in the rocks. Therefore, as a result of this unequal distribution of earth, one hemisphere must always be heavier than the other.
Now the planet also has a center of mass (called by Leonardo, in a terminology that we would not use today, a “center of gravity”). On a homogeneous planet, this “center of gravity” will coincide with the geometric center of the world. But on our actual planet, with one hemisphere heavier than the other, the “center of gravity” will lie below the geometric center and within the heavier hemisphere. The planet, as a living body seeking balance, must strive to bring the center of gravity closer to the geometric center. The earth pursues this goal in a manner known from time immemorial to all riders on seesaws (the Leicester Codex contains a picture of such a seesaw, albeit for a different purpose). To balance a seesaw, the heavier person must move toward the fulcrum at the center, while the lighter person must move farther away. In exactly the same manner, the solid masses of the heavier hemisphere must sink toward the center of the world, while the rocks of the lighter hemisphere must rise. The emergence of mountains from the seas, and the consequent placement of marine fossils on high hills, records this rising of land in the earth’s lighter hemisphere.
Leonardo succinctly describes the general process in Manuscript F (in the Institut de France):
Because the center of the natural gravity of the earth ought to be in the center of the world, the earth is always growing lighter in some part, and the part that becomes lighter pushes upwards, and submerges as much of the opposite part as is necessary for it to join the center of its aforesaid gravity to the center of the world; and the sphere of the water keeps its surface steadily equidistant from the center of the world.
Leonardo must then find a general mechanism for ensuring planetary balance by lightening one hemisphere, while making the other heavier—and he succeeds with two principles, both based on erosion by water: one mode operating in the earth’s interior, the other at the earth’s surface. In the interior, internal veins of water carve out caverns, which eventually become unstable. Their tops finally collapse, and enormous blocks of rock fall all the way to the center of the world. There, the blocks distribute themselves about the center with approximately equal volume in each hemisphere—thus adding weight to one hemisphere and subtracting from the other (for the entire block had previously resided in one hemisphere alone). Leonardo includes a striking illustration of this process in the Leicester Codex—although scholars have failed to recognize the meaning of this figure—showing a fallen block as a large arch neatly draped about the center of the world (see accompanying figure). In describing this internal mechanism in the Leicester Codex, Leonardo explicitly cites the rising of fossiliferous strata as a consequence:
The fact of the summits of the mountains projecting so far above the watery sphere may be due to the fact that a very large space of the earth which was filled with water, that is the immense cavern, must have fallen in a considerable distance from its vault towards the center of the world, finding itself pierced by the course of the springs, which continually wear away the spot through which they pass . . . Now this great mass has the power of falling . . . It balances itself with equal opposing weights round the center of the world, and lightens the earth from which it is divided; and it [the lightened earth] removed itself immediately from the center of the world and rose to the height, for so one sees the layers of the rocks [with their fossils], formed by the changes which the water has undergone, at the summits of the high mountains.
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sp; The exterior method of lightening by erosion can enhance this process once the mountains rise. Rivers will now erode the sides of the mountains and carry the resulting sediment away to the oceans. Some of this sediment will flow to the opposite hemisphere, thus further increasing the imbalance of weight, and causing the mountains to rise still higher as a consequence.
And now these beds are of so great a height that they have become hills or lofty mountains, and the rivers which wear away the sides of these mountains lay bare the strata of the shells, and so the light surface of the earth is continually raised, and the antipodes [the opposite side of the earth] draw nearer to the center of the earth, and the ancient beds of the sea become chains of mountains.
Thus, and finally, we grasp the central importance of Leonardo’s paleontological observations in the Leicester Codex. He featured fossils in order to validate the cherished centerpiece of his premodern worldview—the venerable argument, urged throughout classical and medieval times, for interpreting the earth as a living, self-sustaining “organism,” a macrocosm working by the same principles and mechanisms as the microcosm of the human body. Leonardo required, above all, a general device to make the heavy elements, earth and water, move upward against their natural inclination—so that the earth could sustain itself, like a living body, by constantly cycling all its elements, rather than reaching inert stability with heavy elements in permanent layers below lighter elements.
Leonardo could not find such a mechanism for the chief subject of the Leicester Codex: water—and this failure caused him great frustration. But he succeeded for the even heavier element of earth. He extended a mechanism proposed by Scholastic philosophers for causing the lighter hemisphere of an inhomogeneous planet to rise. He proposed both internal and external erosion by water as processes that could lighten a hemisphere—but he needed observational evidence that land did, in fact, rise. His crowning jewel of confirmation lay in a well-known phenomenon that had provoked intense debate ever since the days of classical Greek science—fossils of marine organisms in strata on high mountains.
Leonardo’s Mountain of Clams and the Diet of Worms Page 4
