394 O. N. Rood on Circular Polarization. 
plate with the plane of primitive polarization I easily obtained 
elliptically polarized light, the axes of the ellipse having any 
desired relation to each other. 
(3.) Through the centres and along the chief diameters of rect 
angular shaped pieces of glass, whose length was four times 
their breadth, the light was also circularly polarized when the 
inclination was 45° to the plane of primitive polarization. When 
two rectangles were crossed at an angle of 45° and placed as 
above, the light was more completely circularly polarized, it was 
found to be right-handed ; upon reversing the inclination of the 
rectangles to each other the beam was turned to the left hand. 
It will be seen therefore that by means of two similar rectan- 
gles of cooled glass, either right or left-handed circular polariza- 
tion may be obtained at pleasure, an observation I believe which 
has never before been made. | 
(4.) The light in all the angles of the octagon was circularly 
polarized. 
8. On the appearance presented by circularly polarizing crystals, de, 
in the Stauroscope. The cross a means of detecting circular or 
elliptical polarization. 
If a plate of quartz be cut at right angles to its axis and of 
such thickness that for example it gives the yellow tint when 
placed in the field of a polariscope, then when introduced into 
the stauroscope it will modify in a certain manner the cross and 
the colored rings. 
(1.) No black cross will be seen in any position of the quartz 
plate; in its place a yellow cross appears which remains statio® 
ary and in its normal position when the quartz is revolved, a 
the white quadrants next to the cale spar cross are replaced 
patches of red and blue color. 
When the analyzing plate is revolved the yellow mrs 
have - placed in the darkened field of a polariscope ; the igh 
remains the same. The circular polariz 
me manner. 
