ARTICLE III. 
Experiments on the Circular Polarization of Light. 
By H. W. Dove. 
From J. C. Poggendorff’s Annalen der Physik und Chemie; Berlin, 
Second Series, vol. v. p. 579. 
1. Circular Polarization of Light by Compressed G'lasses. 
Wuen two systems of waves, of equal intensity, propagated in the 
same direction, and polarized perpendicularly to each other, differ in 
their path by an odd number of quarter-undulations, the particles in 
the resulting system of waves will describe small circles of a similar 
velocity around their points of equilibrium; that is to say, the light will 
be circularly polarized. Every means of equally satisfying these two 
conditions, namely, that of the similar intensity of the system of waves 
polarized perpendicularly to each other, and that of the determinate 
difference of path, consisting of an uneven number of quarter-undula- 
tions, will therefore furnish a method of circularly polarizing light. 
Fresnel and Airy have effected this in different ways. The third mode, 
which I shall here explain, is in practice at least as convenient as those 
hitherto used, and gives moreover a fuller explanation of the phenomena 
_of compressed and cooled glasses in polarized light. 
The condition of the equal intensity of the systems polarized per- 
pendicularly to one another is satisfied by Fresnel by polarizing the 
incident light in a plane which forms an angle of 45° or 135° with the 
_plane of the total reflexion in a glass parallelopiped. The quantities 
of light polarized in, and also perpendicularly to the plane of reflexion, 
are then, according to Fresnel’s formula of intensity, equal to each other. 
He obtains the difference of phases of a quarter-undulation by twice- 
repeated total reflexion, since after a single one under the given cireum- 
stances the periods of vibration of the reflected waves no longer coincide, 
ut exhibit a difference of phases of an 4-undulation. 
The method which Airy has adopted depends upon another principle. 
en a thin plate of an uniaxal crystal cut parallel to the axis, and 
vhose axis forms with the plane of polarization of the incident light 
angle a, is observed through a rhombohedron of Iceland spar, the 
incipal section of which is inclined toward the plane of primitive 
of polarization under the angle 8, then, if I,, I. indicate the intensities 
