The Great Rift by Michael E. Hobart

The Great Rift by Michael E. Hobart

Author:Michael E. Hobart
Language: eng
Format: epub
Publisher: Harvard University Press


FIGURE 10.1.  Adapted from Galileo’s drawing of an ebony chip floating in water. The rectangle CSOI represents a cross section of the lamina, floating slightly below the surface of the water, shown by the line EBAD. The area BCIA is the volume of air that has adhered to the chip.

In the terminology of the day, the issue centered on whether matter should be understood as continuous or contiguous. Generally speaking, Aristotelians believed in the continuity of matter, a belief nested in a series of definitions. “Nature,” the Stagirite had written, denoted a “principle of motion and change,” and motion in turn belonged to a “class” of “continuous” things, which included material bodies that occupied place (local motion was simply a body’s change of place). Regardless of the particular composition of a material body (that is, its particular blend of the elements, earth, air, fire, and water), it remained the same type of matter unless it underwent a series of essential internal or external changes.18 Break a piece of wood into thousands of pieces and each would remain wood. Likewise with water—separate it into thousands of droplets and each is still water. Continuous matter could be cut or divided.

Galileo disagreed, rejecting delle Colombe’s Aristotelian references to water’s continuity as nothing but a “useless multiplication of accidents.” By contrast, he suggested that water be seen as analogous to a collection of separate, contiguous entities, similar to a crowd of people as we walk through it, moving “aside persons already separated and not conjoined,” or to a heap of sand as we thrust a stick into it, merely separating the grains of sand already divided. Galileo précised the point, writing of “two manners” of representing “penetration”: the one in continuous bodies, where division is necessary; the other in “aggregates of noncontinuous but only contiguous parts,” where “there is no need of division, but only of moving.” Water and other fluids, he was “rather inclined to believe” at that moment, were of the latter sort, aggregates of contiguous parts.19

Fire, another of the four fundamental, earthly elements in the Aristotelian view of nature, also offered evidence of aggregate matter composed of contiguous parts. Here Galileo took his initial cue from Democritus (ca. 460–370 BCE), the atomist from antiquity, who had claimed that in water “ascending igneous atoms sustain heavy bodies of broad shape,” while rounder, more narrow bodies of the same material sink. Even though Galileo believed Democritus fundamentally erred in his conviction that shape influenced a body’s buoyancy, he praised him for trying to account for the specific differences between “gravity and levity” with the appeal to fire atoms. Moreover, into this generally philosophical discussion, Galileo proposed an experimental test of heating water and then observing whether a plate would ascend from the bottom of the vessel to the surface. His conclusion? Only in cases involving “exceedingly thin” plates of “material little heavier than water” would the fire atoms actually raise up and sustain a body.20 This was not sufficient evidence to challenge the central



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