Improvements in Angle Trisecting and Bisecting Instruments.

摘要

103,686. Joiner, S. M. Feb. 2, 1916. Dividing-instruments.-An instrument for trisecting, and optionally for bisecting, angles comprises a symmetrical quadrilateral frame of pivoted bars 2 - - 5 having trisecting-bars 12, 13 mounted on a pivot 6 on the axis of symmetry. The diverging ends of these bars are curved and slidably and pivotally connected with the two side members 4, 5 remote from the pivot 6 in such a way that they may be held in any adjusted position. As shown, the quadrilateral is equilateral. In order to set out the axial curve C at the free end of the bar 12, the frame is opened so that the bars 2, 3 enclose a right-angle, and set-screws 16 are so placed on the bars 4, 5 that this angle is trisected by the bars 12, 13, slots in which engage the set-screws 16. With centre 6 and radius 6, 7, a circle is described cutting the axis of symmetry at 9a. With centre 9a, a circle c is described passing through the point 7. With the same radius and with centre 16, an are L' is described. A line L is then drawn parallel with the bar 12 and at a distance from the axis thereof equal to the radius of the circle c, such line cutting the arc L1 in a point L2. With L' as centre, an arc C is then described having the radius of the circle c. Then this arc is the axis of the curved portion of the bar 12 which engages the set-screw 16 when an angle less than a right-angle is being trisected. The instrument is not used for trisecting angles greater than a right-angle; but angles' of any size may be bisected by providing straight, slots 14 in the bars 12, 13 and by mounting a slotted axial bar 9 on the pivots 6, 8