| Max. | Min. | Diff. | Max | Min. | Dif. 
an —— GGG Sa IL ААА 
Cara О | 0.249 | 0.181 | 0068 | 0241 | 0.090 | 0.151 
BE AE | 0298 | 0176 | 0.117 | 0413 | 0111 | 0302 
о at ae he | 1054 | 0.267 | 0.787 | 1221 | 0.243 | 0.978 
This points to two facts: 
1) that the co-efficient of refraction varies much more in the case 
of low-lying lines of vision between points with a small diffe- 
rence of altitude than in the case of lines of vision between 
points, the difference of altitude of which is proportionately 
great, and | 
2) that in the determination of k circumstances make themselves 
felt, which do not, or at any rate not in such a high degree, 
influence the determination of x. 
The cause of both of these circumstances is to be looked for 
in the stratification of the atmosphere. 
x is, as demonstrated, first and foremost dependent upon т. In 
“Meteorologische Terminbeobachtungen am Danmarks Havn”, Medd. 
om Grønland XLII, p.318, WEGENER has made public a thermogram 
which shows how strongly and with what extreme suddenness the 
temperature may oscillate. ; These sudden oscillations of temperature 
of several degrees may suggest the existence of a stratification with 
a great jump in temperature at very nearly the same altitude as 
that of the thermograph. The wave movement which must be sup- 
posed to take place in the strata causes the thermograph to be 
alternately in the colder or warmer stratum. 
In the case of the line of vision at the „Skerry”, the altitude of 
which only varies between 14 and 16 m it is, under these circum- 
stances, easily understood that 7 and so also the co-efficient of re- 
fraction — both x and k — must vary greatly. In the case of the 
lines of vision at Cairn IX and Cairn X a wave movement of this 
kind in the stratification cannot in the same degree influence 7 which 
is, it must be borne in mind, a mean value of the whole stratum 
of air between the Observatory and the cairn. In case the boundary 
between the strata is situated in such a manner that its waves do 
not touch any of the extreme points of the line of vision, it excer- 
cises no influence whatsoever neither on т nor — consequently — 
on x. 
In the case of the lines of vision at the „ЗКеггу” г was deter- 
