Survey of Northeast Greenland. 159 
If we put h, = 0 and z, = 90° we get 
h = Dtan }(z~+ 90°) or 
D = hcot4(z~ 90°) 
The mean value of all the zenith distances at the horizon is 
90°04’04”’, to which corresponds D = about 23.5 km. The greatest 
value of zenith distances to the horizon is 90°06/31”, to which corre- 
sponds D = about 14.7 km. 
The three points at which the levellings were made are in the 
following designated as I, П and Ш. 
The sight at I passed between J. P. Jacobsens © (the “Skerry”) 
and Lille Koldewey, a couple of hundred metres in an easterly 
direction past Kap Christian (see the map: 1:100,000 of Danmarks 
Havn and Environs, Pl. II). The refraction was here often very 
markedly influenced by the nearness of the land. In particular the 
horizon often appeared oblique, in that it lay deeper towards Lille 
Koldewey (see Fig. 20, p. 194). 
The sight at II passed between J. P. Jacobsens @ and Maroussia 
and in such a manner that the distances from the sight to J. P. Ja- 
cobsens Ø and Østre Havnenæs (headland on the east side of the 
harbour entrance’) were equally great. As far as this sight was con- 
cerned, the influence of the nearness of the land was as small as 
possible. 
The sight at III passed in a south easterly direction across Yder- 
bugten (the outer bay). For the first 7 to 8km this sight passed 
across country or between the skerries in Yderbugten. It was often 
distinctly influenced by running closely across the country; more- 
over the land prevented us from seeing the sea horizon, when it lay 
deepest. : 
In spite of the abnormal conditions at I and in particular at III, 
the levellings at these points are, it is to be presumed, of some 
interest, and so I have included them in the subsequent table. On the 
other hand, I have not chosen to compute the co-efficient of refraction 
of the series of observations at I and Ш, but only as far as the 
levellings at II are concerned. To compute k the formula 
re z--90°\? А 4) 
т 
1) The formula may be deduced from the familiar terms of reciprocal, simultaneous 
zenith distances: 
1—k = se + z,-+ 180°) and 
h, +h, = Dtan $(zZ, =z.) = р += 22) 
2 w 
by ‘putting 2, == 90°, ho == 0 andvh = 
XLVI. 1 
