Minutes of proceedings of the Royal Artillery Institution (1858)
Great Britain. Army. Royal Artillery Institution · Woolwich, Eng., : The Institution · leaf 445
e substituted for the slit at Pand an “all-round” image be obtained, as with the telescope. The same arrangement of mirrors can be used for delicate measure- ment of angles, and by its use an angle can be trisected optically in the field. When the instrument is used for measuring angles, a large… … be turned to view an object in some other direction, and the angle between the two lines of direction will be less than the angular displacement of the mirrors from positions perpendicular to the line I P, where the image coincides in direction with the line of direct vision through the slits. Let…
