140 J- Lindhard. 



The effect of the light in the arctic regions is so striking in 

 many ways, that it is a matter for general consideration. Snow- 

 spectacles are necessary, and if these are forgotten the carelessness 

 is very quickly punished with a very troublesome conjunctivitis. 

 On journeys the skin on face and hands soon takes on a dark, 

 copper-red colour, which gradually changes over to lighter or darker 

 brown; on the nose and ears the epidermis peels off in large flakes, 

 and excoriations or blisters occur, which only heal after a long 

 time. As already mentioned, we can also note the effect of the 

 light psychically. In summer in contrast to in winter there is a 

 certain, restless eagerness to work, a reduced feeling of tiredness, 

 which quite agrees with Zuntz and Loewy's descriptions ^ and also 

 with Hasselbalch's experimental results^. 



It is well-known, that the Eskimos like the high-arctic peoples 

 in general have almost as much skin-pigment as the tropical races, 

 a phenomenon which is generally placed in connection with the 

 intensity of the light. 



With regard to the light reflected from the snow, I have only 

 measurements from a single day; but these show quite distinctly — ' 

 even if they naturally can only give an approximate picture of the 

 conditions — that the reflected light is a factor of no small impor- 

 tance. The measurements were taken by Dr. Wegener and myself 

 one day towards the end of April about midday; they showed that 

 the sensitive paper became black 



under as far as possible perpendicular rays in 2 5 sec. 



when the actinometer was held horizontally with the 



plate upwards in 30 sec. 



when the actinometer was held horizontally with the 



plate downwards in 50 sec. 



The maximum intensity of the light is indeed not so great at 



77° N. L. as in the Alps, but as compensation the summer days 



last from the end of April to the end of August. It agrees well, 



therefore, with the explanation put forward, that the result which 



is attained in some few weeks in the Alps requires just as many 



months to appear in Greenland. And when regard is taken of the 



reduced total pressure at high altitudes, which, so far as the carbonic 



acid tension as isolated phenomenon is concerned, undoubtedly 



acts in the same direction as the light, as also to the comparative 



abrupt transition from the lowland to the high land, there is nothing 



remarkable in the fact, that the fall in the carbonic acid tension 



proceeds quickly in the beginning and thereafter more slowly, whilst 



in North Greenland it proceeds comparatively uniformly. 



1 1. с Kap. XVII. - 1. с. 



