362 Morten P. Ровзи.о. 
The tracing-paper slips employed at our Arctic station were 
given to us by Dr. STEENSTRUP; they were of “Leonin-tracing-paper 
No. 173” from Schleicher & Schüll of Düren. According to the 
investigations of Prytz, the absorption-coefficient of this paper is 
0'126, i. e. it allows 0'874 of the light which reaches the paper 
to penetrate it. The power of absorption of the glass-pieces and of 
the glass-tube has, as far as I know, not been investigated. 
The photometer stands more than 10 metres south of the main 
building of the station, about 2 metres above the surface of the 
ground, and is directed vertically upwards (consequently the tube 
is horizontal). The geographical latitude of the place is 69° 14’ 8" 
N. lat. Towards the east and west some low hills are situated at some 
distance from it, towards the north some higher hills, and further 
towards the north high mountains, so that the photometer is never 
directly illuminated by the sun in the azimuth from NW. to N. 
until towards the NE. No more open spot is to be found for miles 
around, and from WIESNER’s investigations we know that in the 
Arctic regions diffuse light plays the most important part. 
The sensitive papers are changed every evening at 6 o'clock. 
There are always two photometers in use as the one brought in 
from the outside cannot, during the cold season, be opened until 
the following day lest the chilled air in the apparatus should cause 
moisture to be instantly deposited upon it. 
With a few exceptions all the readings were taken by my assi- 
stant, Mr. J. N. NYGAARD; in fact he had the whole management of 
the apparatus. I wish particularly to call attention to this fact, 
because two persons do not always read to the same degree, one 
may think he can read yet another degree while the other can read 
no higher. By daily practice Mr. NyGaarp has acquired such a 
degree of accuracy that the individual error may be regarded as 
negligeable. The strips of tracing-paper used were double. In 
the table the numbers on the left indicate that day of the month 
upon which each experiment ended. The highly sensitive paper 
was consequently influenced also by the light of the night before. 
Before I go on to give an account of the results arrived at I 
must, for comparison, mention the light-measurements which have 
already been taken by this method. Dr. STEEnSTRUP had in 1908—04 
taken daily light-measurements both in the Botanic Garden in Copen- 
hagen and upon Anholt, a small island in the Cattegat, and he has 
published the results (see list of literature). Unfortunately the 
measurements were made with another kind of tracing-paper, the 
absorption-coefficient of which — at any rate according to Prytz’s — 
investigations — is 0'145. Consequently, this paper permits less 
