Survey of Northeast Greenland. 227 
cairn by a cursory sight along the telescope. The distance to the 
station cairn would then have to be measured with a measuring 
tape; but this would in any case have to be done out of regard to 
the computation of centration. 
The errors in the levelling, which arose from the fact that the 
measurements were executed to the foot of the cairn were, however, 
insignificant compared with those which might be introduced in 
consequence of variations in the refraction of the atmosphere. This 
circumstance is dealt with more fully in the section on terrestrial 
refraction. Here I shall therefore only draw attention to the fact 
that, when the levelling was performed, I had no knowledge of the 
natural conditions which give a hint of possible anomalies of the 
refraction, and that my observation journal consequently contains 
no remarks which may decide one in estimating discrepancies in 
the results. 
The difference of altitude was computed by the formula 
H-H, = Deotz + 
where D is the distance between the two stations, z the zenith 
distance measured, k the co-efficient of refraction and R the radius 
of curvature of the normal 
segment in H, through H. 
D? 
m Des) = DT | tp) eee | ne 
Siete.) was 4 a A НН 
taken from the present 08200) | 
table, calculated for use 09) 04 | | si A eee 
in Iceland. R is here com- qs iran Osi ns 21 300 | BG 
puted as a mean value of 2 a 03 = = | 31 
the curvature of 65°, and N 2 | 0.5 oA er | 3.2 
in the case of k the value 5 17 0.6 | os 49.5 3 
of 0.1306 found by Gauss 6 | 26 a 26 | 460 | ig 
has been used. In the т 22 at zen, 
; É Sen > DE и 
table D is expressed in 9 55 qi 99 572 | 39 
X | Jr a | .ы | 
kilometres, the other two 10°. 6.8 1.3 30 612 | 4.0 
a — | 15 |— 49 
columns in metres. Я a 65а | 
The starting points of 19 98 15 | зо 697 | +3 
the trigonometric mea- 3 11.5 1.7 | 5% Ta 
3 1.8 : 4.6 
suring of altitudes were 1% 13.3 Sal se nn 
the termini of the base г. я м KR 4.9 
| 16 56 SEO m: 
(stations I and II) the alti- 17 19.7 22 Sy 931 | +9 
tudes of which, by means 18 22.1 a | 38 98.3 | = 
of geometrical levelling, er = 6 | 89 ne Br 
Е 2 27.2 = 2) 8.5 
were determined at 14.27 m | 2.8 | å Q 
and 11:26 т. 
