points where a perpendicular plane upon the line i-a would pass through it, the points in the circumference of the cone, as indicated by the projectors i', 2', 3', etc., will also be points in the required ellipse. Only one mould is shown ; another is required for the outer face, but the procedure is exactly the same, the superimposing of it on the drawing would only confuse the reader.
Chapter VI ISOMETRIC PROJECTION
Derivation of Term Isomctric. Theory of Isometric Projection —advantages of tlie method. To construct a Parish's Scale. A Simple Isometric Scale. Equal Angle Projection — its principles. Mechanical Method of Construction. The Isomctric Planes. Example»—a Nest of Shelves. Mortise and Tenon Joint. Non-rectangular Figures. Projecting an Octagonal Prism. An Octagonal Pyramid. A Splayed Washing Tray. A Gallows Bracket. A Dvrarf Cupboard. A Brick Quoin and Footings—how bricks should be laid. A Builder's Gantry- -method of construction, how to project. A Draper's Counter- -details oi construction, method of making the projection. Circles and Curves—how they may be rendered in isometric. Projecting a Cylinder. Isomctric View ot a Moulding
Isometric projection, or "projection showingequal measurements," as it was described by tlie inventor, Professor Parish, of Cambridge Univ ersity, derives its name from two Greek words ; isos, equal, and metron, a measure, referring to the fundamental principle of the method : that the axial or root lines of the drawing, although reduced, are equal in length or measure, and, therefore, proportionate to the object. One of the chief advantages of this method of drawing is that direct measurements may be taken from the isometric axes or root lines of the drawing just as in orthographic drawings. A further advantage is that three views of the object are combined in one drawing, thus giving it an appearance of solidity that is very convincing; we are, however, pract ically limited to one position only, as will be better understood by inspection of the examples than by a written description.
The basis of isometric projection is the relative positions
Figs. I and 2. Isometric Scales. Fig. 3. Diagram illustrating Theory. Fig. 4. The Isometric Axes. Fig. 5. Orthographic Projections of the Cube. Fig. 6. Isometric Projection by Means of Set Square. Fig. 7. Inverse Isometric Projection. Fig. 8. A Box. Fig. 9. A Cube resting on one Edge. Fig. 10. The Isometric Planes
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