M. G. Quincke on Diffraction, 369 



ization is perceived, which with the same angle of incidence 

 and the same spectrum of the second class is different in amount, 

 and the absolute value of which may become greater or less as 

 the wave-length increases. To an azimuth +a or —a of the 

 incident light corresponds after the diffraction the same azi- 

 muth -f- ft or — /3 of the transmitted or reflected light. For the 

 directly transmitted or reflected rays (corresponding to the dif- 

 fraction-angle 0°) the rotation of the plane of polarization 

 may amount to a few minutes or several degrees — with the 

 lateral maxima of the second class, to 90° or more. The more 

 frequent case is where the amplitude polarized perpendicular 

 to the principal diffraction-plane, or parallel to the lines (fur- 

 rows) of the grating, is greater for blue than for red light. 



5. A grating inserted between Nicol prisms or polarizing ap- 

 paratus, when the incident light is white, imparts to the directly 

 transmitted or reflected light similar colours to those shown by 

 plates of crystal between polarizing arrangements. 



6. Ratio of amplitude and difference of phase vary, under 

 otherwise like conditions, with the inclination of the grating to 

 the incident rays. 



7. Ratio of amplitude and difference of phase change, for nor- 

 mal as well as for oblique incident rays, with the substance of 

 which, with transmitted light the surface of the bars, with re- 

 flected light the furrows or elevations of the grating consist. 



8. The amplitude-ratio and phase-difference change with the 

 width of the apertures or the form of the furrows or elevations. 



9. The finer the grating, or the more it is inclined to the in- 

 cident rays, the greater, cteteris paribus, is the change produced 

 by diffraction in the ratio of amplitude and the difference of 

 phase of the light-waves polarized parallel and perpendicular to 

 the principal plane of diffraction. 



10. The light reflected from furrowed metallic mirrors directly 

 in the principal diffraction-plane exhibits very nearly the same dif- 

 ference of phase as with smooth mirrors of the same material. 

 The amplitude polarized parallel to the reflection- or principal 

 diffraction-plane predominates still more over the amplitude po- 

 larized perpendicular to the plane of incidence than with unfur- 

 rowed metallic mirrors. The direct reflected light from fur- 

 rowed metallic mirrors approaches nearer in its properties to 

 that reflected from transparent substances than does that which 

 is reflected from smooth unfurrowed metallic mirrors. 



11. With gratings in other respects alike, the phenomena 

 vary with the substance in which the diffraction takes place. 



12. The secondary maxima, for which the theory does not 

 account, exhibit the same remarkable behaviour towards polar- 

 ized light as the maxima of the second class. 



Phil. Mag. S. 4. Vol. 45. No. 301. May. 1873. 2 B 



