TWO:Ren rolled down the roof to a long ledge that the light had shown him. If he could run along that he could gain the next house, and go a deal further. Then he might slip down another ladder, and so through a sleeping household to safety. He rocked unsteadily over on the ledge with his feet hanging perilously over the parapet; the next instant one of the police officers, at the risk of his neck, was upon him. Ren would have wriggled for his knife, but he dared not move.The means of supporting cores must be devised, or at least understood, by pattern-makers; these supports consist of 'prints' and 'anchors.' Prints are extensions of the cores, which project through the casting and extend into the sides of the mould, to be held by the sand or by the flask. The prints of cores have duplicates on the patterns, called core prints, which are, or should be, of a different colour from the patterns, so as to distinguish one from the other. The amount of surface required to support cores is dependent upon their weight, or rather upon their cubic contents, because the weight of a core is but a trifling matter [96] compared to its floating force when surrounded by melted metal. An apprentice in studying devices for supporting cores must remember that the main force required is to hold them down, and not to bear their weight. The floating force of a core is as the difference between its weight and that of a solid of metal of the same sizea matter moulders often forget to consider. It is often impossible, from the nature of castings, to have prints large enough to support the cores, and it is then effected by anchors, pieces of iron that stand like braces between the cores and the flasks or pieces of iron imbedded in the sand to receive the strain of the anchors.
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