GUNN. ISACHSEN. [2nd ARC. EXP. FRAM 



I. 



Description of the Astronomical and Surveying Instruments. 



JLhe Expedition took with it the following instruments for astro- 

 nomical and surveying observations: 



1. A large altazimuth by Olsen & Co. of Christiania. This instru- 

 ment was also used on the Fram Expedition of 1893—96. It was 

 damaged by an accident before the Expedition reached its first winter 

 quarters, and could not be repaired with the means at our disposal. 



2. Two smaller altazimuths, marked No. 1 and No. 2, also by Olsen 

 & Go. The telescope, the axis of which is broken by a reflecting prism, 

 has an aperture of 25 mm., a focal length of 20 cm., and a magnifying 

 power of 15 diameters. Both the circles have a diameter of 12 cm., 

 are divided into 20', and are each read by 2 verniers that give 30". 

 The verniers of the vertical circle can be made level by means of a 

 spirit-level; and there is a second spirit-level on the alidade of the iiori- 

 zontal circle. The angular value of one division of the levels is 15". 

 There is no screw with pinion for the adjustment of the focus of the 

 telescope for different distances; the adjustment is made by hand, and the 

 eye-piece fixed with ordinary screws. This arrangement, inconvenient 

 as it is when the instrument is to be used for triangulation, had the 

 effect of keeping the optical axis accurately adjusted, even on the sledge- 

 journeys; and the treatment that an instrument of this description is 

 liable to receive on such journeys is anything but gentle. In the course 

 of the four years, both the objective and the eye-piece end had almost 

 worn through the wooden sides of the instrument-case. 



There is no special stand for this instrument, but it can be fixed 

 to the top of the case by means of a hook, the case itself being then 

 placed upon the snow, while the observer is in a lying position. On 

 most of the journeys, however, a plane-table was taken, and the instru- 

 ment simply placed upon it. 



3. An ordinary ship's sextant by Heckelmann, Hamburg, reading 10". 



4. Two small pocket-sextants. 



