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4 FIRST PRINCIPLES OF with the object beneath it, the visual rays from all its principal points being projected on that plane in points which are afterwards joined by right lines. Such a view when obtained is called a "sectional plan," the plane of its projection being the original HP, the position of the object only with respect to that plane having been reversed. A similar plan of the object whose projections are figured 3, 3, in Fig. 96, will have quite a different appearance to that given of it in Fig. 97. It is, we are told, a hollow wooden tube, whose thickness is shown in its end elevation on the VP. When looked at from above, in the direction of the arrow, its appearance is the same as if it were merely a rectangular prism of solid material throughout, with its sides inclined to the HP : but if a cutting plane be caused to pass through it horizontally from end to end, it would then be seen (on the removal of the part cut off) that its interior is hollow, and its "sectional plan" something very different from that before obtained. What that view would be we shall see later on. 25. Now, in addition to the simple plan and front elevation of an object being given, it is necessary, before its exact shape and construction can be understood, to have one or more " side views " or side elevations of it, for there is hardly anything in mechanical constructions, at any rate which is of the same shape when viewed from the side and end. To show how such views are obtained, let VP and HP in the sketch (Fig. 98) represent the two planes of projection, as before, in their normal position that is, at right angles to each other and let it be assumed that the YP is in two parts, A and B, hinged together at c d, and that the part A is capable of being swung