Rarefaction and Condensation
Rarefactions and condensations, in their simplest form, are those phenomena in which material substances vary in their densities, becoming more fine or tenuous on the one hand or coarser or thicker on the other. Although they might seem unproblematic concepts to modern readers, in fact they have a complex history and even have been seen as fundamental aspects of nature. For a number of thinkers, the phenomena of rarefactions and condensations seemed to suggest, inescapably, that matter must have inbuilt principles of activity. Essentially, this boils down to a belief that matter can determine its own dimensions in some way – either by spreading itself out, or contracting itself inwards, or, in the case of corpuscular theories, by moving its constituent particles closer together or further apart. And this kind of self-determination or self-movement was, for these thinkers, either occult or fundamental and unexplained. It is a sign of the complexity of the issues arising from condensation and rarefaction that alternative, non-occult, attempts to explain these phenomena never achieved full consensus. The most influential account was eventually provided by Isaac Newton by supposing attractive and repulsive forces capable of acting at a distance between atomic particles. But even this was superseded by the non-occult kinetic theory of gases in the late nineteenth century.
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