188 I. P. Koch. 
sufficient to determine the daily rate, in a manner which is fairly 
accurate in all details, the figure, however, very clearly and with 
great certainty shows the main characteristics of this rate. These 
main characteristics — a pronounced minimum in the afternoon and 
a pronounced maximum during the night — which are common to 
the line of vision across land and across water, are in no particular 
different from what is 
CII known: from other part 
ee ae ee | u. 
of the globe; in the case 
Bl 
BREMEN RES 
of the line of vision at 
Cairn X, I shall in parti- 
cular draw attention to 
the characteristic feature 
that the co-efficient of 
refraction in the hours 
immediately before noon 
and as late as at 1P keeps 
fairly constant, which 
phenomenon is also well- 
known in Europe. 
It has been proved, on 
an earlier occasion, that 
the curve of the variation 
of the co-efficient of re- 
fraction may, under a cer- 
FE GS ge в м er 8 10 0 2 4 6 tain reservation, directly 
Fig. 15. Diagram of the daily rate of the co-effi- be looked upon as a curve 
cient of refraction. The ordinates indicate the 
Ak's with the same value as given in the table 
above. variation of и. 
according to the altitude). 
On the Danmark-Ekspedition we did not succeed in proving, by 
means of a direct measurement of temperature, the existence of a 
С ae GLE 
daily rate in ав’ 2 Consequence of the fragmentary nature of the 
measurements of temperature and disturbances by aperiodic changes’). 
Through the determination of the daily variation of the co-efficient 
„ 
- 
И 
a 
= 
= 
Les 
Seine 
BEN Ber 
BEE 
9) 
= 
7 
= 
Eis 
5 
= 
CSE 
Ра 
Я Tree 
— 100 
of the variation of ar (the 
: ь : : aT 
of refraction a corresponding and simultaneous movement in 4; may 
be considered as proved, as far as the lowest strata of the air are 
concerned. 
The circumstance that the daily rate of the co-efficient of re- 
1) See remark in Brand: Die Temperatur in der Ausguckstonne: Medd. om Grenl., 
XLII, p. 591. 
