XVIII GEELMUYDEN. ASTRONOMICAL OBSERVATIONS. [NORW. POL. EXP. 
It a be the azimuth of the star at the moment of observation, reckoned 
from south through west, as computed from the given declination, latitude 
and clock error, 
A= 180° +a+itgh t+csech 
will be the azimuth, from north through east, corresponding to the circle rea- 
ding S for the star; here h is the apparent altitude of the star, the double 
sign of ¢ corresponding to obj. right and obj. left. 
It has not been necessary to take account of the collimation. For the 
high stars the effect is eliminated in the mean, as the observations were taken 
in both positions of the instrument and the altitudes were nearly the same 
on both occasions. This is, however, not visible from the circle-readings, which 
ought to differ by about 180°, but do not do so, the observer having always 
added 180° to the second circle-reading. When the small altazimuth was used 
the difference of 180° has been retained. 
For some low stars, observed only in one position of the instrument, the 
effect of collimation will be very nearly the same as for the terrestrial mark, 
supposing both to have been observed in the same position of the objective 
relative to the observer, which has not always been expressly stated. 
The accuracy of angle-measuring with the magnetic theodolite being infe- 
rior to that of the large altazimuth, a few seconds of are are of no impor- 
tance in the determination of azimuth. 
The values of the angle C—S-+ 4A, where C is the circle-reading for the 
mark in the magnetic observatory, were transmitted to Mr, Steen for applica- 
tion in the reduction of the observations of declination. 
On several occasions the Sun was observed directly with the magnetic 
theodolite. 
Lieut. Scort-Hansen also made a great number of independent determi- 
nations of the magnetic declination by means of the azimuth compass, which 
was for this purpose mounted on the ice at a distance of at least 60 paces 
from the ship. The observations then consisted in simply noting the time 
when the Sun or a star passed the plane of the sights, and reading off the 
card of the compass. The reduction of these observations does not call for 
any further remark. 
Most of the azimuth-observations have been computed by Mr. ALEXANDER 
and Mr, GraaRup. 
