| 摘要 |
<p>The pair of compasses for drawing ellipses has two arms (3, 13) each with a pointed lower end (11, 12), and joined by a link (21) at their upper ends. The arm (3) is fitted with a circular disc (1) which can be clamped in any position in a longitudinal slot and inclined at any angle. A third arm (6), which carries a pencil point, pivots about the upper end of the arm which carries the disc so that as it rotates it is guided by the edge of the disc. The pencil point thus traces out an ellipse which is an enlarged and vertically projected view of the inclined disc.</p> |
