( 608 ) 
haze, like a piece of frosted glass, had an appreciable depolarizing 
influence on the transmitted light. 
An investigation about the influence of haze on polarized light 
has been taken in hand in the physical laboratory at Utrecht, but 
has not yet been finished. As the result of preliminary experiments 
we can only mention here that most probably the measures of the 
polarization of the light of the corona have only slightly been 
disturbed by the presence of clouds. If the sky had been clear, 
the main results would have been the same. 
II. Heat-radiation of the corona. 
In a much higher degree than the light-rays the dark heat-rays 
are intercepted by clouds and haze. The conditions were thus - 
very unfavourable for the measures of radiation, and this circum- 
stance is so much the more to be regretted since the observations 
have shown that in clear weather the ratio between the total radi- 
ation of the corona and the total radiation of the uneclipsed sun 
would undoubtedly have been successfully determined. 
The method of observation was very simple. A very sensitive 
small thermopile (consisting of 8 couples of alloys of bismuth whose 
total exposed surface occupied a circle of 5 mm. diameter) was 
exposed without the intervention of either lenses or mirrors to the 
radiation of a circular patch of sky of 3° diameter. 
The apparatus was mounted parallactically and could easily be 
kept in such a direction that the eclipsed (or non-eclipsed) sun 
remained in the centre of the field of 3°. 
If we take as unit the radiation which will give a deviation 
of one scale-division, when the resistance in the circuit and 
the sensibility of the galvanometer have the same values which 
they actually had during the pointings on the corona, then the 
strongest radiation we observed during our stay in the camp 
is represented by the number 1941000. On clear days (e. g. 
on the 6th of May) the observations ran very regularly. At 7h58m 
a. m. (in this section of the report we use civil time) of that day 
the radiation was 1457000; it increased with small oscillations 
caused by invisible haze to 1902000 at 12h Om, 
Not quite so regular but still very satisfactory were the readings 
on the fairly clear days of the 14%, 15th and 16th of May. On the 
17% no observations were made on account of the heavy clouds, 
ee ese 
