With the
declination axis in an approximately horizontal position the place
where the pointer cuts the horizon is noted. The declination axis
is then turned through 180 deg., when the pointer should again cut
at the same place. Proper adjustment will cause it to do so. It is
desirable that the hour circle should read approximately zero when
the declination axis is horizontal, but this is not necessary for
a reason soon to be explained. All these adjustments, once
carefully made, need not be changed.
In using the instrument the hour axis can be directed to the north
pole by the following method. Point it approximately to the north
star. The pole is 1 deg. and 15 min. from the star on a straight
line from the star to "Mizar," the star at the bend of the handle
in the Big Dipper. Turn the hour circle into a position where the
pointer can describe a circle through "Mizar." Only a rough
setting is necessary. Now turn the pointer so that a reading of 88
deg. 45 min. shows on the declination circle on that side of 90
which is toward "Mizar." When this is done, clamp both axes and
turn the shafts in the base until the pointer is directed
accurately to the north star.
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