370 MORTEN P. PORSILD. 
of the intensity of the different rays according to the different alti- 
tudes of the sun. — 
The Altitude of the Sun | 90° | 30° |19°.4 |14°-5 |11°-5 | 9°-6 | 89.2 | 79.1 
Red Ал = 760лл ..... 0.90 | 0-80 | 0-72 | 0-64 | 0-58 | 0-52 | 0-46 | 0.42 
Orange D À = 590 ..... | 0-82 | 0-68 | 0:55 | 0-45 | 0-37 | 0-30 | 0-25 | 0-20 
Blue GA 430... 0:66 | 0:42 | 0-29 | 0.19 | 0-12 | 0-08 | 0:05 | 0-04 
Violet HA = 400 ...... 0-54 | 0-30 | 0-16 | 0-09 | 0-05 | 0-02 | 0-01 | 0-01 
Consequently we see, that by help of the photographic method, 
even after only a few years of observation, an approximate conception 
may be obtained of the chemical light-totals during winter in the 
Polar regions. But from this we dare not draw any conclusions as 
to the visible light nor, from this method, can we acquire any 
knowledge of the circumstances pertaining to the cloud-screen during 
the winter of the Arctic regions. 
Exact time of the Maximum of the Annual Intensity. 
In his work “Der Lichtgenuss der Planzen” Wiesner draws up 
the following statements concerning the light-climate in Vienna. 
(1) In Vienna the period January—June shows a smaller light- 
total than the period July—December. 
(2) The first: half of our period of vegetation, March—June, 
shows a smaller light-total than the other half, July—October. 
(3) Both the spring months, March and April show a somewhat 
smaller light-total than the autumn months September and October. 
(4) The period May—June is poorer in light than the period 
July—August. 
As may distinctly be seen from Tables III—IV these statements 
do not correspond with the fact in northern countries. Already 
in both the Danish series we have seen the reverse to be the 
case, and even more markedly so in the Arctic series. WIESNER, 
also, mentions (1. с.) that in St. Petersburgh the annual maximum 
occurs in the first ten days of June, and as the curve for the altitude 
of the sun is symmetrical, these differences cannot be dependant 
upon its position and the reason for them must be sought in purely 
climatic circumstances pertaining to the cloud-screen. Here I must 
briefly recall the course of the seasons in South Disco. From 
January to about the middle of April the sea is covered with con- 
tinuous ice, and the ground everywhere with snow; the climate is 
very continental and the cloud-screen slight. At the end of April 
