stand substantially at the intersection of the plane of the meridian with the equatorial plane this being the line to the equatorial zenith as shown in fig1 and 2 when the device is mounted on base 25 at any other latitude axis 7 will stand substantially at the intersection of the plane of the meridian with the plane of that latitude substantially parallel to the equatorial zenith line at that meridian meridian sunbeam 23 fig1 and 1a has a declination about 23 u00b0 30 39 north of the equatorial zenith sunbeams parallel to sunbeams 23 will have substantially the same declination with respect to axis 7 at any latitude when the device is so mounted and thus the latitude vector will be eliminated from the meridian declinations of all sunbeams received by reflecting surface 12 at any latitude fixed axis 9 lying in the plane of the meridian parallel to the upper surface of base 25 will thus remain substantially parallel to the polar axis of the earth at any latitude movable axis 10 rotating about axis 9 in a plane perpendicular to axis 9 will thus lie in a plane substantially parallel to the equatorial plane of the earth at any latitude and the orientation of reflecting surface 12 with respect to axis 9 and to the plane of rotary motion of movable axis 10 at any instant during the motions herein specified will be substantially.