ination axis, are tightened. Then the pointer is
carefully turned through 180 deg. and if it is not again directed
to the same point, it is not perpendicular to the declination
axis. When properly set it will describe a great circle. 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. It is evident from a study of the
picture that the position of the small pointer which indicates the
reading on the hour circle is not independent of the way in which
the tripod or pipe is set up. It would then be useless to adjust
it carefully to zero when the pointer cuts the "zenith" as is done
with a large equatorial. Instead, the adjustment is made by
setting the clock or watch which is part of the outfit. The
pointer is directed to Alpha, Cassiopiae, and the hour reading
subtracted from 24 hours (the approximate right ascension of the
star) gives the time which the clock should be set to indicate.
All of these settings should require not more than five minutes.

To find a star in the heavens, look up its declination and right
ascension in an atlas. Set the declination circle to its reading.
Subtract the clock time from the right ascension (plus 24 if
necessary) and set the hour circle to the result. The star will
then be seen on the tip of the pointer.

To locate a known star on the map, turn the pointer to the star.
Declin