Vill GEELMUYDEN. ASTRONOMICAL OBSERVATIONS. — [NORW. POL. EXP. 
during the last year (from the autumn of 1895) the right microscope for the 
vertical circle seems, however, to have got somewhat out of adjustment, the 
difference between the two readings being generally about 20” and in some 
cases reaching 30”. As there are not sufficient data to take this difference 
into due consideration it has been necessary to take the simple mean in all 
cases. When it happened that a division-line was near the middle of the 
field of the microscope, the observer often pointed the micrometer wires to a 
line on each side, and the mean of the three was then taken. 
The telescope has an aperture of about 5 cm. and 42 em. focal length. 
It was provided with two eyepieces giving magnifying powers of about 30 
and 40. The optical axis is broken by a reflecting prism and the eyepiece 
placed at one end of the horizontal axis. The illumination of the field comes 
from a lamp at the other end of the axis. The wires in the focus are fine 
lines engraved on glass. There was a set of 13 wires (vertical in the hori- 
zontal position of the telescope) but only the middle wire and the horizontal 
wire were used for the observations. 
The striding level of the horizontal axis is divided from the middle; one 
division = 4”. As this level must always be read off in the two opposite 
positions, the sum of the two differences will give the inclination of the axis 
in seconds, 
1896, May 6, it was noticed by Capt. Sverprup that the motion of the 
telescope about the horizontal axis was not quite independent of that of the 
alidade; when the screw working on the arm of the latter was turned (in 
order to get the bubble of the level in a convenient position) it had an effect 
of some seconds on the pointing of the telescope. Lieutenant Scort-HANsEN 
took the instrument on board, loosened the parts and cleaned them, but the 
error was still perceptible in some positions of the instrument. It is of course. 
only when the screw is touched between the pointing of the star and the 
reading of the microscopes and level, that this can introduce an error in the 
observation, but Mr. Scorr-Hansen is of opinion that such an error may occur 
in some of the observations from the winter 1895—96. Before the cleaning 
of the instrument he made some experiments in order to ascertain the amount, 
and found the maximum effect to be about 50”. 
This instrument is at present on board the Fram on Capt. SvERDRUP’S 
expedition to Greenland, 
