Leonardo’s Mountain of Clams and the Diet of Worms (5 page)

He read the Greek masters Aristotle and Theophrastus on geology; he owned a copy of Pliny’s encyclopedic
Natural History;
he studied the views of the great Islamic scholars Avicenna and Averroes (mainly via medieval Christian
sources). He listed parts of what he had read and owned on the inside front cover of his Manuscript F—Aristotle’s
Meteorologia
, Archimedes on the center of gravity, “Albertuccio and Albertus
de coelo et mundo
.” I found this last comment particularly sweet, as Leonardo follows medieval conventions in distinguishing his sources as “Little Al” (the Italian diminutive Albertuccio) and “Big Al.” Little
Al is Albert of Saxony (ca. 1316–1390), the German Scholastic philosopher and physicist. Later scholars frequently confused him with Big Al, or Albertus Magnus (ca. 1200–1280), Albert the Great, the teacher of Saint Thomas Aquinas. Both Als wrote extensively about the form and behavior of the earth, and Leonardo probably learned the views of Jean Buridan (1300–1358) by reading Albert of Saxony’s
discussion. Buridan’s concept became the basis for the theory of the earth that Leonardo defended with his observations on fossils.

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:

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:

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.

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:

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:

(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.)