XIV GEELMUYDEN. ASTRONOMICAL OBSERVATIONS. [NORW. POL. EXP. 



In summer time only the Sun was available for observation. These 

 altitudes were mostly taken with the sextant, but some also with the altazi- 

 muth. The results of these observations, especially the clock error, are 

 generally subject to greater uncertainty than those of the winter observations, 

 by reason of the interval of several hours between the determinations of 

 latitude and time. While in many cases the time could be safely computed 

 by means of the latitude deduced from the nearest meridian altitude, it was 

 in other cases necessary to allow for the drift of the ice, and the interpolation 

 necessary for this purpose is of course always somewhat uncertain. When 

 the latitude was determined by extra- meridian altitudes the same remark 

 applies, so that sometimes repeated corrections were necessary. Only in a 

 few cases was the clock error determined by equal altitudes of the Sun, 

 which were, for the same reason, generally treated as absolute altitudes. In 

 some cases when a series of circum-meridian altitudes had been taken, the 

 moment of apparent noon could be deduced with sufficient approximation 

 from the differences, and thus the time be determined as well as the latitude. 

 In some few cases, when two or more altitudes of the Sun had been taken 

 near the prime vertical, one of the computers, Mr. ALEXANDER, has with 

 advantage employed the differences for determination of latitude. 



Some observations taken with the altazimuth during the last summer 

 (1896) have been treated in the same manner as the star observations, thus 

 neglecting the drift in the interval. 



Occasionally altitudes of very low stars or a low Sun were measured 

 in connection with the ordinary determination of time and latitude, especially 

 during severe cold, in order to determine the refraction. 



For the reduction of altitudes measured with the sextant from the natural 

 horizon it was deemed most correct to form a table for the dip, adapted to 

 the peculiar circumstances, though the difference from the values ordinarily 

 used are not of importance. The expression for the dip of the horizon may 

 be written 



where S = 206 265", H is the height of the eye, p the average radius of 

 curvature for the part of the earth under consideration, and k the constant 

 of terrestrial refraction. The theoretical expression for this constant contains 



