NO. 6.| INTRODUCTION. INSTRUMENTS. IX 
A small altazimuth by Olsen. The circles have diameters of 10 cm. 
and are graduated to half degrees, two opposite verniers giving the single 
minutes. The relative movement of circles and reading-apparatus is the same 
as in the larger instrument. A fixed level, placed parallel to the vertical 
circle, was read off on measuring altitudes, but its position was not such 
that it can be considered as an alidade-level. It is divided from the middle 
in parts of 0/8. The telescope, whose axis is broken by a reflecting prism, 
has an aperture of 2 cm, a focal length of 16 cm., and a magnifying power 
of 12. The wires in the focus consist of one horizontal and two vertical 
lines (about 4’ apart) engraved on glass. 
This instrument was not much used on board but followed Mr. Nansen 
on his sledge expedition. 
A sextant by Hechelmann, of the usual construction, giving the angles 
to 10’. Usually the altitudes were measured from the ice as a natural 
horizon or over a basin of mercury as an artificial horizon. On some few 
occasions a glass horizon by Negretti & Zambra was used; the level which 
was read off in its two positions, when placed in the vertical plane of the 
celestial object, was divided to 2/6. There was also another glass horizon 
with aluminium mounting, by Porter, which was only used 1893 September 
28 and October 2; its level was divided to 3’.9. Occasionally a trough of 
tar or a pool of water on the ice was used as an artificial horizon. 
The astronomical telescope was almost invariably used. 
A small pocket sextant by Cary, London, was used by Mr. Nansen on 
his sledge expedition. The limb, of radius 4.5 em., is divided to half degrees, 
the vernier giving single minutes. The instrument is made of aluminium 
which did not, however, prove to be a good metal for this purpose, the 
screws becoming immoveable from oxidation. 
Several compasses, among them an azimuth-compass by Hechelmann 
with 8 small needles suspended by silk wires. The card, divided to degrees, 
has a diameter of 21 cm. The reading of the card was always made both 
ways, the eye being held in the plane through the vertical and the horizontal 
wire of the diopter-apparatus, either before the thread or before the slit. 
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