3 
places, i.e. monocularily.(Fig.?) 
If one wants to inves- 
tigate the proportion of the 
sunlit parts of the ground 
within a stereoscopio model 
of a wooded area, one only has 
to put up à third lamp in such 
  
a way, that its light is direc- 
ted towards the model-forest 
from the same direction as na- 
tural sunlight. Those parts of 
the ground, that are sunlit Visible in stereo 
and visible in stereo, are il- : Monocularily visible 
luminated by all three lamps, #8 Not visible 
and the parts illuminated by Fig.5 
the sun-lamp and one of the camera-lamps are monocularily vi- 
sible in the model. 
In the same way one can study the influence of the 
altitude of the sun. 
Fig. 4 shows how the experiment was performed. 
In Pj and P2 two lamps were placed at a distance corre- 
sponding to the base on scale 1:200, P1 and P2 - the two 
exposure-locus of an air-camera. On the floor a grid was 
marked, wich covered one fourth of the stereocovered part 
of the floor. The model-forest was placed on the points Al, 
A2, A5... A155; Bl, B2, Blesesses B15; C1 etc. The lamps 
were turned on and the photographic paper was exposed. 
After development and fixing the area of the double-illumi-