Survey of Northeast Greenland. 173 
The refraction conditions in the line of vision 
Observatory— Cairn X. 
| | | | Vertical 
Date Hour D 250.0342 Te | x k | movement 
il i | | | м x 3 
12 August... 8230 | 735.5 | 0.0389 | 2181 | 0.249 | 0.241 | not observed 
PA ER 8200 | 743 0.0365 | 274.9 | 0.242 | 0.216 | not observed 
| 11800 | 7445 | 00326 | 2724 | 021 | 0118 | 1 
8. Sept | 2250 | 732 0.0314 | 2716 | 0.210 | 0.090 | 1 
12. — ....| 9330 | 727 .| 0.0302 | 2706 | 0202 | 00% | 0 
15. — ....| 3220 | 733.5 | 0.0329 | 2660 |‘ 0.230 | 0.100 | 1 
И. — ....| 2550 | 730.5 | 0.0263 | 267.6 | 0.181 | 0.088 | 1 
10. October. | 1250 | 725 ° 0.0336 | 259.8 | 0.243 | 0.158 Le 
в (15303 | 74 0.0610 | 262.8 | (0.443) | (0.246) | 3 
Mean.. | 0.222 | 0.138 
the line of vision to the “Skerry” is concerned, х is computed with 
comparative certainty at 0.520, whereas for the line of vision at 
Cairn IX we found x — 0.234 with rather less certainty. In the 
first case we have a line of vision, nearly exclusively traversing 
water at a mean altitude of 15m; in the second case the line of 
vision exclusively traverses land, but along the coast, at a mean 
altitude of 97 m. This change in the position and altitude of the 
line of vision causes a change of x to the extent of about 0.29! 
After this one must suppose that to the line of vision at Cairn X, 
which traverses land and the mean altitude of which is 222 m, must 
correspond a ie which is considerably smaller than eras and con- 
sequently also, that the value of x = 0.222 computed above, and 
corresponding to the line of vision at Cairn X is too great. 
It might seem that the difference 0.222 — 0.138 — 0.084 (see 
table above) under these conditions is not very marked. It must, 
however, be remarked that ke being determined at 0.160 the x corre- 
sponding to this value should be about 0.222 + (0.160 — 0.138) — 
about 0.242, whereas for the line of vision at Cairn IX by a similar 
consideration we should get the value of 0.237. It would be absurd 
to suppose that the co-efficient of refraction for the line of vision 
at Cairn IX should not be greater than for the line of vision at 
Cairn X. The consideration shows that the material for a comparison 
between x and k is not sufficiently comprehensive, as has already 
been stated several times. 
That which in the first place aroused my interest in a compu- 
tation of the values x was the idea of controlling, in this manner 
the values of Е. and ke resting on the few reciprocal, simultaneous 
zenith distance observations, thus in this case of the value k* — 1100 
