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THREE:The glowing enthusiasm of Plato is, however, not entirely derived from the poetic traditions of his native city; or perhaps we should rather say that he and the great writers who preceded him drew from a common fount of inspiration. Mr. Emerson, in one of the most penetrating criticisms ever written on our philosopher,129 has pointed out the existence of two distinct elements in the Platonic Dialogues��one dispersive, practical, prosaic; the other mystical, absorbing, centripetal. The American scholar is, however, as we think, quite mistaken when he attributes the second of these tendencies to Asiatic influence. It is extremely doubtful whether Plato ever travelled farther east than Egypt; it is probable that his stay in that country was not of long duration; and it is certain that he did not acquire a single metaphysical idea from its inhabitants. He liked their rigid conservatism; he liked their institution of a dominant priesthood; he liked their system of popular education, and the place which it gave to mathematics made him look with shame on the ��swinish ignorance�� of his own countrymen in that respect;130 but on the whole he classes them among the races exclusively devoted to money-making, and in aptitude for philosophy he places them far below the Greeks. Very different were the impressions brought home from his visits to Sicily and204 Southern Italy. There he became acquainted with modes of thought in which the search after hidden resemblances and analogies was a predominant passion; there the existence of a central unity underlying all phenomena was maintained, as against sense and common opinion, with the intensity of a religious creed; there alone speculation was clothed in poetic language; there first had an attempt been made to carry thought into life by associating it with a reform of manners and beliefs. There, too, the arts of dance and song had assumed a more orderly and solemn aspect; the chorus received its final constitution from a Sicilian master; and the loftiest strains of Greek lyric poetry were composed for recitation in the streets of Sicilian cities or at the courts of Sicilian kings. Then, with the rise of rhetoric, Greek prose was elaborated by Sicilian teachers into a sort of rhythmical composition, combining rich imagery with studied harmonies and contrasts of sense and sound. And as the hold of Asiatic civilisation on eastern Hellas grew weaker, the attention of her foremost spirits was more and more attracted to this new region of wonder and romance. The stream of colonisation set thither in a steady flow; the scenes of mythical adventure were rediscovered in Western waters; and it was imagined that, by grasping the resources of Sicily, an empire extending over the whole Mediterranean might be won. Perhaps, without being too fanciful, we may trace a likeness between the daring schemes of Alcibiades and the more remote but not more visionary kingdom suggested by an analogous inspiration to the idealising soul of Plato. Each had learned to practise, although for far different purposes, the royal art of Socrates��the mastery over men��s minds acquired by a close study of their interests, passions, and beliefs. But the ambition of the one defeated his own aim, to the destruction of his country and of himself; while the other drew into Athenian thought whatever of Western force and fervour was needed for the accomplishment of its205 imperial task. We may say of Plato what he has said of his own Theaet��tus, that ��he moves surely and smoothly and successfully in the path of knowledge and inquiry; always making progress like the noiseless flow of a river of oil��;131 but everywhere beside or beneath that placid lubricating flow we may trace the action of another current, where still sparkles, fresh and clear as at first, the fiery Sicilian wine.

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THREE:Irregularity of cooling may be the result of unequal conducting power in different parts of a mould or cores, or it may be [98] from the varying dimensions of the castings, which contain heat as their thickness, and give it off in the same ratio. As a rule, the drag or bottom side of a casting cools first, especially if a mould rests on the ground, and there is not much sand between the castings and the earth; this is a common cause of unequal cooling, especially in large flat pieces. Air being a bad conductor of heat, and the sand usually thin on the cope or top side, the result is that the top of moulds remain quite hot, while at the bottom the earth, being a good conductor, carries off the heat and cools that side first, so that the iron 'sets' first on the bottom, afterwards cooling and contracting on the top, so that castings are warped and left with inherent strains.

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THREE:Milling relates to metal cutting with serrated rotary cutters, and differs in many respects from either planing or turning. The movement of the cutting edges can be more rapid than with tools which act continuously, because the edges are cooled during the intervals between each cut; that is, if a milling tool has twenty teeth, any single tooth or edge acts only from a fifteenth to a twentieth part of the time; and as the cutting distance or time of cutting is rarely long enough to generate much heat, the speed of such tools may be one-half greater than for turning, drilling, or planing tools. Another distinction between milling and other tools is the perfect and rigid manner in which the cutting edges are supported; they are short and blunt, besides being usually carried on short rigid mandrils. A result of this rigid support of the tools is seen in the length of the cutting edges that can be employed, which are sometimes four inches or more in length. It is true the amount of material cut away in milling is much less than the edge movement will indicate when compared with turning or planing; yet the displacing capacity of a milling machine exceeds that of either a lathe or a planing machine. Theoretically the cutting or displacing capacity of any metal or wood cutting machine, is as the length of the edges multiplied into the speed of their cutting movement; a rule which applies very uniformly in wood cutting, and also in metal cutting within certain limits; but the strains that arise in metal cutting are so great that they may exceed all means of resisting them either in the material acted upon, or in the means of supporting tools, so that the length of cutting edges is limited. In turning chilled rolls at Pittsburg, [141] tools to six inches wide are employed, and the effect produced is as the length of the edge; but the depth of the cut is slight, and the operation is only possible because of the extreme rigidity of the pieces turned, and the tools being supported without movable joints as in common lathes.Forging relates to shaping metal by compression or blows when it is in a heated and softened condition; as a process, it is an intermediate one between casting and what may be called the cold processes. Forging also relates to welding or joining [77] pieces together by sudden heating that melts the surface only, and then by forcing the pieces together while in this softened or semi-fused state. Forging includes, in ordinary practice, the preparation of cutting tools, and tempering them to various degrees of hardness as the nature of the work for which they are intended may require; also the construction of furnaces for heating the material, and mechanical devices for handling it when hot, with the various operations for shaping, which, as in the case of casting, can only be fully understood by experience and observation.

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