384 Prof. R. W. Wood: Some new : 
contact with the glass. ‘The reflected beams were found 
to be plane-polarized, the vibrations being in the directions 
shown in fig. 5 a, for an angle of incidence near the pola- 
rizing angle. As the angle of incidence increased, the planes 
of the two vibrations both turned towards the vertical, and 
finally made an angle of 90° with eack other, 7. e. 60° and 
30° with the reflecting surface. 
If we compound the two components shown in fig. 5a 
with varying phase-differences, we can account easily for the 
polarized fringes. In ie: Oo ‘leh BO bp the vibration from 
the glass and BA that from the metai. When the path is 
zero or a whole number of waves, we have the piane-polarized 
resultant BE. If the path-difference is an odd number of 
half-waves, we have the plane- polarized resultant BF. These 
two states occur along the lines 1, 5 and 3, 7 respectively. 
The angles which the planes of vibration make with the 
reflecting surface should be respectively greater and less 
than the angle made by the component coming from the 
metal, as was ‘found to be the case. As we increase the angle 
of incidence the component BC (from giass) increases in 
magnitude and turns up towards the vertical, the inclinations 
of the planes of polarization of the two sets of fringes to each 
other becoming greater. 
Between the lines along which the light reflected from the 
film is plane-polarized, we have lines “of elliptically (or in 
some cases circularly) polarized light. The directions of 
revolution were determined with the quarter wave-plate, and 
are as shown in fig. 4. Geometrical computations of the 
elliptic vibrations, resulting from two components such as 
are shown in fig. 5 b , agreed perfectly with the experimentally 
determined orbits, both in respect to the directions of the 
major axes and the directions of rotation. The method 
used was REALE to the one given in Miiller-Pouillet’s text- 
book ::(vol? tis al. ppditss), ote only modification necessary 
being the raion of one of the sets of parallel lines, which 
represent displacements, through a certain angle, since, in 
the case with which we are dealing, the two components are 
not at right angles. By sufficiently j increasing the incidence- 
angle the components AB and BC can, however, be brought 
to very nearly a right angle. At the same time the intensity 
of the component from the glass surface has increased to such 
a degree as to be about equal to the one from the metal, 
and we have practically circular polarization along certain 
lines. 
A careful study of these fringes makes a most excellent 
exercise for advanced students in Optics. The conditions 
