Das vorliegende Bum ist die erweiterte Ausarbeitung einer Vor lesung, die der Verfasser an der Universitat Freiburg i. Br. wahrend des Wintersemesters 1968/69 fUr Horer alIer Fakultaten gehalten hat. Einzelne Teile gehen nom weiter auf einen Vortrag des Ver fassers vor der Wissensmaftlichen GeselIsmaft zu Freiburg im November 1967 zurUdt, der in der Serie der Freiburger Universi tatsreden veroffentlimt worden ist. In der jetzigen, erweiterten Fassung wendet sich das Bum an alle naturwissensmaftlim interessierten Laien, denen es nimt nur darum zu tun ist, auf billigem Wege Wissensstoff zu...

Sect. 13. 203 and the geometric elements for the large orbit are re-computed. From the analysis it cannot be decided whether the third body is close to the visual primary or secondary component; this can only be decided by measuring the orbital motion on an astrometric background of other stars (Chap. IV). In accurate long-term problems the perspective change in the apparent orbit due to motion of the center of mass in the line of sight, must be taken into account. In the future this feature of orbital analysis will undoubtedly become more and more important. An example of the required...

139 long ago that, when an extended source of unpolarised light is viewed through a highly dichroic crystalline plate cut normal to one of the optic axes, two dark brushes-the BREWSTER'S brushes-are seen. In the interference between crossed polaroids the dark isogyres do not in general pass through the optic axial directions as they do in the case of transparent crystals. These phenomena can be broadly explained using the approximate theory mentioned in Sect. 43 where the waves propagated along any direction are taken to be linearly polarised. We have seen however that according to the...