GB238275A - Improvements in or relating to optical instruments - Google Patents

Abstract

238,275. Ionides, A. C., and Gordon, J. W. May 5, 1924. Levels; sextants; theodolites. - Reflector systems comprising two facing mirrors at an inclination to one another in combination with an additional mirror, which may be a single plane mirror or two plane mirrors at right-angles with fixed or adjustable angular relation to the first mentioned two mirrors, present two separate images to the eye of an observer and are utilized for reading angular magnitudes and are applied to several optical instruments, e.g. levels, sextants, &c. In one form, Figs. 1 and 3, two inclined mirrors a are combined with a plane mirror b, which lies at right-angles to the axis of symmetry 1 - - 1 of the mirrors a. This form will reflect into the eye of an observer, two views of a distant object one laterally reversed with respect to the other, the views only coinciding along the principal axis, which serves as a fiducial line of any instrument to which the system is applied. The plane mirror b may occupy a central position as shown in Fig. 2, separating the upper and lower portions of the view observed in the inclined mirrors a. In a modification one of the inclined mirrors a may be replaced by two mirrors at 45‹ to the horizontal and to the plane mirror b. As applied to a pendulum level the system is mounted as shown above the pivot of the pendulum j which is supported on gimbal rings, and damped by liquid in a container k<2>. A rod l<4> is provided to lift the pendulum off its supports and simultaneously to close the container k<2>. The reflecting system is arranged to show the level by a horizontal fiduciary line given by coincidence of two views, one laterally inverted. A surveyor's level is shown in Fig. 20 in which the reflecting system p<4> is mounted beneath a telescope p<5> upon the ordinary stand. As applied to a sextant, Figs. 13 and 14, the facing mirrors a<3>, a<4> are parallel to one another and to the zero position of the adjustable mirror b<3>. The mirror a<3> covers one half of the object glass and the index glass b<3> is of such a height that the reflected rays are received by the other half of the object glass of the telescope a. The mechanism for adjusting the glass b<3> is on the hinder face of the instrument, rough adjustment being effected by the wheel n<1> and fine adjustment by the wheel n<7>. In the modified square shown in Figs. 18 and 19, the plane mirror b, Fig. 2, is replaced by two mirrors b<5>, b<6> at right-angles, placed symmetrically.