FORE:Inherent or cooling strains in castings is much more intricate than shrinkage: it is, in fact, one of the most uncertain and obscure matters that pattern-makers and moulders have to contend with. Inherent strains may weaken castings, or cause them to break while cooling, or sometimes even after they are finished; and in many kinds of works such strains must be carefully guarded against, both in the preparation of designs and the arrangement of patterns, especially for wheels and pulleys with spokes, and for struts or braces with both ends fixed. The main difficulty resulting from cooling strains, however, is that of castings being warped and sprung; this difficulty is continually present in the foundry and machine-shop, and there is perhaps no problem in the whole range of mechanical manipulation of which there exists more diversity of opinion and practice than of means to prevent the springing of castings. This being the case, an apprentice can hardly hope for much information here. There is no doubt of springing and strains in castings being the result of constant causes that might be fully understood if it were not for the ever-changing conditions which exist in casting, both as to the form of pieces, the temperature and quality of metal, mode of cooling, and so on.Evidently this kind of thing had happened before, and this was the fee usually paid. Bruce slipped the money in his pocket, feeling that he had earned it. The guide picked up a Bradshaw from the table and indicated Dover therein. Two strapped portmanteaus were on the floor.

FORE:The arrangement of patterns with reference to having certain parts of castings solid and clean is an important matter, yet one that is comparatively easy to understand. Supposing the iron in a mould to be in a melted state, and to contain, as it always must, loose sand and 'scruff,' and that the weight of the dirt is to melted iron as the weight of cork is to water, it is easy to see where this dirt would lodge, and where it would be found in the castings. The top of a mould or cope, as it is called, contains the dirt, while the bottom or drag side is generally clean and sound: the rule is to arrange patterns so that the surfaces to be finished will come on the bottom or drag side.49

FORE:Well may M. Havet say of the Academicians: ��ce sont eux et non les partisans d��Epicure qui sont les libres penseurs de l��antiquit�� ou qui l��auraient voulu ��tre; mais ils ne le pouvaient pas.��250 They could not, for their principles were as inconsistent with an absolute negation as with an absolute affirmation; while in practice their rule was, as we have said, conformity to the custom of the country; the consequence of which was that Sceptics and Epicureans were equally assiduous in their attendance at public worship. It is, therefore, with perfect dramatic appropriateness that Cicero puts the arguments of Carneades into the mouth of Cotta, the Pontifex Maximus; and, although himself an augur, takes the negative side in a discussion on divination with his brother Quintus. And our other great authority on the sceptical side, Sextus Empiricus, is not less emphatic than Cotta in protesting his devotion to the traditional religion of the land.251For the restrictions under which Aristotle thought were not determined by his personality alone; they followed on the logical development of speculation, and would have imposed themselves on any other thinker equally capable of carrying that development to its predetermined goal. The Ionian search for a primary cause and substance of nature led to the distinction, made almost simultaneously, although from opposite points of view, by Parmenides and Heracleitus, between appearance and reality. From that distinction sprang the idea of mind, organised by Socrates into a systematic study of ethics and dialectics. Time and space, the necessary conditions of physical causality, were eliminated from a method having for its form the eternal relations of difference and resemblance, for its matter the present interests of humanity. Socrates taught that before enquiring whence things come we must first determine what it is they are.322 Hence he reduced science to the framing of exact definitions. Plato followed on the same track, and refused to answer a single question about anything until the subject of investigation had been clearly determined. But the form of causation had taken such a powerful hold on Greek thought, that it could not be immediately shaken off; and Plato, as he devoted more and more attention to the material universe, saw himself compelled, like the older philosophers, to explain its construction by tracing out the history of its growth. What is even more significant, he applied the same method to ethics and politics, finding it easier to describe how the various virtues and types of social union came into existence, than to analyse and classify them as fixed ideas without reference to time. Again, while taking up the Eleatic antithesis of reality and appearance, and re-interpreting it as a distinction between noumena and phenomena, ideas and sensations, spirit and matter, he was impelled by the necessity of explaining himself, and by the actual limitations of experience to assimilate the two opposing series, or, at least, to view the fleeting, superficial images as a reflection and adumbration of the being which they concealed. And of all material objects, it seemed as if the heavenly bodies, with their orderly, unchanging movements, their clear brilliant light, and their remoteness from earthly impurities, best represented the philosopher��s ideal. Thus, Plato, while on the one side he reaches back to the pre-Socratic age, on the other reaches forward to the Aristotelian system.