(9) At the point where a line of force intersects the perpendicular **bisector** of the axis r=r'=r o, say, and cos 0 - cos 0 obviously =l/r o, l being FIG.

If the centre of S'N' is on the perpendicular **bisector** of SN, 0 = Zir, and the couple will be MM 'cos cp/r 3, (20) tending to increase 4); this is the " broadside on " position.

**Bisector**, from bi-, two, secare, to cut), in geometry, the same as **bisector**, i.e.

A point which divides a line, or a line which divides an angle, into two equal parts; in crystallography it denotes the **bisector** of the angle between the optic axes.

If now a line be drawn from A to the **bisector** H of the side BC, it will meet the vertical through G in I and IJ =c(cos a+a sin a)/ur.

5) is the direction of a ray, either from a heavenly body or from a terrestrial point, impinging at 0 upon the surface of quicksilver, and reflected in the direction OR, the vertical line is the **bisector** OZ, of the angle POR.

In the case of a biaxal plate perpendicular to the **bisector** of the acute angle between the optic axes, the curves of constant retardation are approximately Cassini's ovals, and the lines of like polarization are equilateral hyperbolae passing through the points corresponding to the optic axes.