Survey of Northeast Greenland. 179 
3 
— 
Cairn X: kX = 0.160 | Cairn IX: KR =0. 
Cairn У 
т 
Skerry |Horizon II 
kS —0.516 kl! —0.584 
determin. 
of T 
k k 
Number of 
determin 
of + 
| > 
я 
Number of 
k 
m 
| 
ти т 
Aug. 23rd—Oct.21st. | kX-+-0.004 +0.0014 34 |№Х-+0.001 --0.0004 28 | AY +-0.059 KS +-0.175) ки, 
in which К and т vary. The necessary data for the computation of 
х corresponding to the given values of 7 are to be found in Medd. 
om Grønland XLII. In this case one can, however, not expect 
agreement between k and x, because the mean values given are 
based on a comparatively small number of single determinations of 
k and 7, which furthermore generally occur on different days. 
The summary shows that the refraction, as was to be expected, 
varies somewhat differently in the case of lines of vision across 
land (IX and X) than in the case of lines of vision across water 
(V, the “Skerry”, Horizon II). However it is common to all of the 
five lines of vision that the co-efficient of refraction is greatest 
during the real summer season. This is the opposite of what is 
known from the other places, where the co-efficient of refraction is 
greatest during the winter. An explanation is consequently needed. 
First of all it must be remarked that as observations of the 
refraction at Danmarks Havn during the months of winter and 
spring are lacking 
en SA bp А ВИ ВЕ 
co-efficient of refrac- 0 FEE TFT | 
eer A rt 
tion has not also a 
maximum during the ne feb Harz. Apr-May.June July Aug Sept. Cet. Nov. Dec.Jan. 
winter or spring. This Fig. 14. Yearly rate of the difference in the temperatures 
is undoubtedly the at 5 m and 200 m above the sea. 
case. Fig. 14, which 
is reproduced from the often mentioned work of WEGENER: “Drachen- 
und Fesselballonaufstiege” shows the yearly rate of the difference 
of temperature between 5 m and 200 m altitude. The curve may be 
directly looked upon as representing the yearly rate of 7 — = in 
the interval in question. The curve shows that corresponding to 
the coldest time of the year there is a maximum of (in conse- 
quence of the strong irradiation during the winter), and we must 
suppose that to this corresponds a maximum of k. Whether this 
May 31st— June 22nd | k* -+-0.030|+0.0011 24 | kX!+-0.037|-+0.0002, 21 1x\,-+0.038| kS +0.156| kl! 40.186 
July 9th--Aug. 12th . rs +-0.030)+0.0062 29 | kX+0.034 +0.0014 21 | kY +0.072) kS +0.178) ki +-0.359 
0.203 
