VIII 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 cm. 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. SVERDRUP 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 SCOTT-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. SCOTT-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 From on Gapt. SVERDRUP'S 

 expedition to Greenland. 



