FORE:Protagoras was born about 480 B.C. He was a fellow-townsman of Democritus, and has been represented, though not on good authority, as a disciple of that illustrious thinker. It was rather by a study of Heracleitus that his87 philosophical opinions, so far as they were borrowed from others, seem to have been most decisively determined. In any case, practice, not theory, was the principal occupation of his life. He gave instruction for payment in the higher branches of a liberal education, and adopted the name of Sophist, which before had simply meant a wise man, as an honourable title for his new calling. Protagoras was a very popular teacher. The news of his arrival in a strange city excited immense enthusiasm, and he was followed from place to place by a band of eager disciples. At Athens he was honoured by the friendship of such men as Pericles and Euripides. It was at the house of the great tragic poet that he read out a work beginning with the ominous declaration, I cannot tell whether the gods exist or not; life is too short for such difficult investigations.66 Athenian bigotry took alarm directly. The book containing this frank confession of agnosticism was publicly burned, all purchasers being compelled to give up the copies in their possession. The author himself was either banished or took flight, and perished by shipwreck on the way to Sicily before completing his seventieth year.An apprentice may get a clear idea of this venting process by inspecting tubular core barrels, such as are employed in moulding pipes or hollow columns, or by examining ordinary cores about a foundry. Provision of some kind to 'carry off the vent,' as it is termed by moulders, will be found in every case. The venting of moulds is even more important than venting cores, because core vents only carry off gas generated within the core itself, while the gas from its exterior surface, and from the whole mould, has to find means of escaping rapidly from the flasks when the hot metal enters.
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