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.
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 also needed to assert that the elevation of strata with fossils must represent a general and repeatable feature of the earth’s behavior, not an odd or anomalous event. Thus he had
to refute the two explanations for fossils most common in his time—for Noah’s flood could only be viewed as a strange and singular phenomenon, and if all fossils derive from this event, then paleontology illustrates no general mechanism for the rising of land. And if fossils grow as objects of the mineral kingdom within rocks, then the mountains may always have stood high, and we can derive no
evidence for any uplift at all. Thus Leonardo made his superb observations on fossils in order to validate his lovely, but ever so antiquated, view of a causally meaningful and precise unity between the human body as a microcosm and the earth as a macrocosm. Leonardo, the truly brilliant observer, was no spaceman, but a citizen of his own instructive and fascinating time.
I like to contemplate
Leonardo, this complex man of peace, of gentleness, of art, of scholarship; this military engineer who designed (but generally did not build) ingenious instruments of war, but who would not reveal his ideas for a submarine, as he stated in the Leicester Codex:
This I do not publish or divulge on account of the evil nature of men who would practice assassinations at the bottom of the seas, by
breaking the ships in their lowest parts and sinking them together with the crews who are in them.
And I like to compare his views on the mechanism for raising mountains from the sea (and exposing fossils for collectors) with our most celebrated literary image on the same subject—Isaiah’s prophecy that “every valley shall be exalted.” I also recall the peace that shall reign on Isaiah’s mountain
(festooned, no doubt, with fossils), where a scholar might study the raising of earth to his heart’s content, and not need to provide his warlike patron with plans for the raising of sieges or the razing of enemy cities. Isaiah’s summit, where “the wolf also shell dwell with the lamb, and the leopard shall lie down with the kid . . . They shall not hurt nor destroy in all my holy mountain.”
2
THE
GREAT WESTERN
AND THE FIGHTING
TEMERAIRE
S
CIENCE PROGRESSES
;
ART CHANGES
. S
CIENTISTS ARE INTERCHANGEABLE
and anonymous before their universal achievements; artists are idiosyncratic and necessary creators of their unique masterpieces. If Copernicus and Galileo had never lived, the earth would still revolve around the sun, and earthlings would have learned this natural truth in due time.
If Michelangelo had never lived, the Sistine Chapel might still have a painted vault, but the history of art would be different and humanity would be a good deal poorer. This “standard” account of the differences between art and science belongs to our distressing but prevalent genre of grossly oversimplified dichotomies—stark contrasts that both enlighten in their boldness and distort in their formulaic
divisions of complexly intertwined entities into two strictly separated piles—“and never the twain shall meet, / Till Earth and Sky stand presently at God’s great Judgment Seat.”
The supposed inexorability of technological progress, under this distorting dichotomy, leads to the myth of science as virtually disembodied—a machine endowed with its own momentum, and therefore striding forward almost
independently of any human driver. Scientists, under this model, become anonymous and virtually invisible. A few names survive as icons and heroes—Edison and Bell as doers, Darwin and Einstein as thinkers. But, if we accept the premise that technological innovation (in manufacturing, warfare, transportation, and communication) has powered social change far beyond all other consequences of human
emotion and ingenuity, how can we resolve the paradox that the people most responsible for propelling human history remain so invisible? Who can name anyone connected with the invention of the crossbow, the zipper, the typewriter, the Xerox machine, or the computer?
Artists, politicians, and soldiers win plaudits and notoriety, though so many impose themselves only lightly and transiently upon
the motors of social change. Scientists, engineers, and technologists forge history and gain oblivion as a reward—in large part as a consequence of the false belief that individuality has little relevance when a progressive chain of discoveries proceeds in logical and inexorable order. Let me illustrate our different treatment of scientists versus statesmen and artists with two pairings.
Colonel
Calverly, head of a company of dragoon guards in Gilbert and Sullivan’s
Patience
, introduces his troops by giving the audience a formula for their construction:
If you want a receipt for that popular mystery,
Known to the world as a heavy dragoon,
Take all the remarkable people in history,
Rattle them off to a popular tune
. . .
The Colonel then rips off (at patter-song speed) two hilarious
doggerel verses, listing thirty-eight historical figures, including a few fictional and general characters. Only one is a scientist. (The notoriously sexist Gilbert listed three times as many women—Queen Anne, the generic and demeaning “Odalisque on a divan,” and Madame Tussaud, founder of the great London wax museum.) The scientist appears in the first quatrain:
The pluck of Lord Nelson on
board of the
Victory—
Genius of Bismarck devising a plan
—
The humor of Fielding (which sounds contradictory)
—
Coolness of Paget about to trepan.
Most of us will have no trouble with the first three—Admiral Horatio Nelson dying at the battle of Trafalgar, the great German statesman, and the author of
Tom Jones.
But scientists gain little recognition in their own times and quickly fade from
later memory. So who is Mr. Paget, about to open his patient’s skull? Sir James Paget, surgeon to the queen and a founder of the science of pathology, may have been a household name to his Victorian contemporaries, but few of us know him today (and I couldn’t have made the identification without my trusty encyclopedia). So scientists and engineers create history, but Gilbert chooses only one to
participate in the construction of English fiber, and even this man has since sunk to oblivion in the general culture of educated people.
For the second pairing, let us return to Admiral Nelson and the story of Trafalgar. On October 21, 1805, Nelson’s fleet of twenty-seven ships met and destroyed a combined French and Spanish force of thirty-three vessels off Cape Trafalgar, near the Strait of
Gibraltar. Nelson’s forces captured twenty ships and put 14,000 of the enemy out of commission (about half killed or wounded, and half captured), while suffering only 1,500 casualties and losing no ships. This victory ended Napoleon’s threat to invade England and established a supremacy of British naval power that would endure for more than a century.
Nelson, “on board of the
Victory
,” engaged
his flagship with the French
Redoutable.
The opposing ship fired at such close range that a French sniper, shooting from the mizzentop of the
Redoutable
, easily picked off Nelson from a distance of only fifteen yards. Nelson died of this wound a few hours later, but with secure knowledge of his triumph.
Nelson’s ship, and much of the battle, was saved by the second man-of-war on the line, the
Temeraire.
This vessel rescued the
Victory
by firing a port broadside into the
Redoutable
and disabling the French ship. (The mainmast of the
Redoutable
fell right across the
Temeraire;
the French ship then surrendered, and the
Temeraire
’s crew boarded her and lashed the defeated vessel to her port side.) Another French ship, the
Fougueux
, then attacked the
Temeraire
, but the British man-of-war
fired her starboard broadside, to equally good effect, and secured her second prize, lashed this time to her starboard side. The
Temeraire
, now disabled herself, but with her two prizes lashed to her sides, had to be towed into port by a frigate.