Leonardo’s Mountain of Clams and the Diet of Worms by Stephen Jay Gould Read Free Book Online

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, likethe 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 operatebest 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 proposalwon’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 mechanicalterms:
    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 themountains 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 thisresolution 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 couldbe 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 ofideas 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 homogeneousand 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