( 606 ) 
The appended diagram (Plate III) gives a summary of the times 
of exposure of the coronagraphs and the prismatic camera. 
C. Physical observations. 
I. The polarization of the light of the corona. 
The aim of the observations of polarization was to measure the 
proportion of polarized light in as many well determined points of 
the corona as possible. 
The observations have been made in an excellent manner by 
lieutenant T. J. vAN DER Escm and four assistents. 
Before the day of the eclipse the observers had repeatedly practised 
on an artificial corona, under circumstances as similar as possible 
to those which were expected during the eclipse. This artificial corona 
gave in the telescope an image of about the same size as that of 
the real corona; its light was partly polarized in radial planes, while 
the proportion of polarized light could be altered at will, so that 
control was possible. The observers got so well in practice that 
they were able to measure the proportion of polarized light on 12 
arbitrarily selected points within 6 minutes, and to read off the 
coordinates of these points. 
A few minutes before the beginning of totality, as well as afew 
minutes after the end, the diffused light of the sky round the sun 
Fig. 1. 
(at a distance of about one diameter from the sun’s limb in the direct- 
ions North, East, South and West) was analyzed to decide whether 
