In the doxographical tradition the concept of a ‘crystalline’ outer-heaven is ascribed to two Presocratic thinkers. Aëtius tells us that Anaximenes held that the stars were fastened like nails in the ‘crystalline’: and, again, that Empedocles believed that the fixed stars were attached to the ‘crystalline’, while the planets were unattached: The ascription of this concept to both these Presocratic philosophers is decidedly odd; for, whereas, in the case of Empedocles’ thought, fire acts as a solidifying agent, Anaximenes, on the (...) other hand, connected solidity with cold and rarity with heat and in his cosmology the heavenly bodies are created by the rarefaction into fire of vapour from the earth. For this reason the concept of a solid outer-heaven is quite incompatible with the little else that is known of his cosmogony and cosmology. (shrink)