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THREE:Cores are employed mainly for what may be termed the displacement of metal in moulds. There is no clear line of distinction between cores and moulds, as founding is now conducted; cores may be of green sand, and made to surround the exterior of a piece, as well as to make perforations or to form recesses within it. The term 'core,' in its technical sense, means dried moulds, as distinguished from green sand. Wheels or other castings are said to be cast in cores when the moulds are made in pieces and dried. Supporting and venting cores, and their expansion, are conditions to which especial attention [95] is called. When a core is surrounded with hot metal, it gives off, because of moisture and the burning of the 'wash,' a large amount of gas which must have free means of escape. In the arrangement of cores, therefore, attention must be had to some means of venting, which is generally attained by allowing them to project through the sides of the mould and communicate with the air outside.The history of Neo-Platonism, subsequently to the death of Plotinus, decomposes itself into several distinct tendencies, pursuing more or less divergent lines of direction. First of all, it was drawn into the supernaturalist movement against which it had originally been, in part at least, a reaction and a protest. One sees from the life of its founder how far his two favourite disciples, Amelius and Porphyry, were from sharing356 his superiority to the superstitions of the age. Both had been educated under Pythagorean influences, which were fostered rather than repressed by the new philosophy. With Porphyry, theoretical interests are, to a great extent, superseded by practical interests; and, in practice, the religious and ascetic predominates over the purely ethical element. Still, however great may have been his aberrations, they never went beyond the limits of Hellenic tradition. Although of Syrian extraction, his attitude towards Oriental superstition was one of uncompromising hostility; and in writing against Christianity, his criticism of the Old Testament seems to have closely resembled that of modern rationalism. But with Porphyry��s disciple, Iamblichus, every restraint is thrown aside, the wildest Oriental fancies are accepted as articles of belief, and the most senseless devotional practices are inculcated as means towards the attainment of a truly spiritual life.