MARYLAND GEOLOGICAL SURVEY 523

Hence, to obtain the hour angle of Polaris subtract the time of
upper culmination from the correct local mean time of observation;
the remainder will be the hour angle of Polaris.

The observation will be made as directed under Method I, modified
as follows: there will be no waiting for the star to reach elongation;
the observation may be made at any instant when Polaris is visible,
the exact time being carefully noted.

TABLE XVII.

This table gives, for various hour angles, expressed in mean solar
time, and for even degrees of latitude from 36 to 40 degrees, the
azimuths of Polaris during the remainder of this century, computed
for average values of the north polar distance of the star—the argu-
ments (reference numbers), being the hour angle (or 23h. 56m.1,
minus the hour angle, when the latter exceeds 11h. 58m.), which is
termed the Time Argument;¹ and the latitude of the place of obser-
vation. The table is so extended that azimuths may be taken out by
mere inspection and all interpolation avoided, except such as can be
performed mentally.

The hours of the " time arguments " are placed in the columns
headed " Hours," on the left. The minutes of the time arguments
will be found in the columns marked " m.," under the years for which
they are computed, and they are included between the same heavy
zigzag lines which inclose the hours to which they belong.

¹ The vertical diameter SS', Fig. 9, divides the apparent path of Polaris
into two equal parts, and for the star at any point s_t on the east side, there
is a corresponding point s on the west side of the meridian, for which the
azimuth Nw is equal to the azimuth Ne. The are SSiS'Sa, taken from the
entire circle (or 23 h. 56.1 m.), leaves the are Ss_e, and its equal, Ss_lt expressed
in time, may be used to find, from Table XVII, the azimuth NIC, which is
equal to Ne.

The hour angles entered in Table XVII include only those of the tcest half
of the circle ending at S', and when an hour angle greater than 11 h. 58 m.
results from observation, it will be subtracted, from 23 h. 56.1 m., and the
remainder will be used as the " time argument " for the table. The sur-
veyor should not confound these two quantities. The hour angle itself
always decides the direction of the azimuth and defines the place of the star
with reference to the pole and meridian, as noted at top of Table XVII. See
examples at the end of this part.