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COMMENTARY
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equally clear from his account that the word normally had the same significance.
19. some thin\ that pumice is formed entirely as a result of burning.
The ancients apparently made little or no distinction between true combustion and otlier high-temperature phenomena, as was mentioned in the notes on section 14. Evidently fire was a term that included all phenomena involving light and a high temperature. Therefore, when Theophrastus speaks of the origin of pumice from burning, combustion is not to be understood, but rather the formation of this material in the usual way by the expulsion of gases from molten lava. Superficially, of course, this process sometimes closely resembles actual combustion, especially when, as often happens, the gases evolved in the volcanic action take fire.
19. with the exception of the \ind that is produced from the foam of the sea.
The pumice that was thought to be produced from foam is clearly the same as the floating pumice still found around the shores of islands in the Aegean Sea. Such pumice emanates from the active volcanic island of Thera (Santorin), where considerable quantities are to be seen floating on the surface of the water. Theophrastus evidently believed that it was formed in some way from the foam of sea water. This notion may have been obtained from Aristotle, for in a treatise On Plants usually ascribed to the latter, a theory is advanced to explain how floating stones could be formed from sea water.92 According to the author93 of this treatise, such stones were produced by the violent collision of one wave with another. First of all, foam is produced which congeals with the consistency of oily milk. When the water is dashed against sand on a beach, the sand collects the fat part of the foam, which dries with an
92 De Planus, Π, 823Β.
93 Though this treatise is included in the corpus of Aristotelian writings, there is considerable doubt that Aristotle was the actual author. It appears to be a later production of the Peripatetic school, and there is some possibility that Theophrastus, or a pupil of Theophrastus, was the real author.
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• 93 *
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