Light; a course of experimental optics, chiefly with the lantern . Fig. 188. -Uni-axial Crystal Circularly Polarised. first position ; the successive appearances being representedin Fig. 188, A, B, c. J The appearances in a bi-axial, such as nitre, are analogousand beautiful, all brushes having vanished, and each axisbeing surrounded by unbroken rings (E, Plate VII.). Andlastly, at the point when the rings are perfect and unbroken,if either the crystal stage, with all it bears—crystal, quarter-wave plate, and analyser—or even only the quarter-wave plateand analyser, be rotated, no change whate
Light; a course of experimental optics, chiefly with the lantern . Fig. 188. -Uni-axial Crystal Circularly Polarised. first position ; the successive appearances being representedin Fig. 188, A, B, c. J The appearances in a bi-axial, such as nitre, are analogousand beautiful, all brushes having vanished, and each axisbeing surrounded by unbroken rings (E, Plate VII.). Andlastly, at the point when the rings are perfect and unbroken,if either the crystal stage, with all it bears—crystal, quarter-wave plate, and analyser—or even only the quarter-wave plateand analyser, be rotated, no change whatever occurs; the ringsremain unbroken, and all trace of polarising planes, as theory : SPIRAL A CaLcrite . D Thin. Siire,in-Tvi^hly carvirer^ent light. B Sijigle AaeU €ff Sugar. E Arra^OTixte, Ditto XVI.] UNBROKEN RINGS. 337 would lead us to expect, is completely lost. The mostmarked demonstration of this is to rotate the whole affairwith a crystal of nitre, or arragonite; as nothing canmore strikingly show the perfect independence of any planesof polarisation than the fact that such a bi-axial, whichordinarily changes so greatly (see D, E, F, Plate V.), whenthe crystal itself is rotated till its two axes stand at 45°,shows no change whatever when rotated as described. Theperfect rings round the two axes rotate round each other, butremain in all positions unaltered. It may be worth while to remark, that a circular chilledglass in the optical stage behaves exactly like a uni-axialcrystal in the crystal stage, under circularly-polarised next the polariser a quarter-wave plate, and then thechilled glass, the usual black cross is replaced by the thinnebulous grey
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Keywords: ., bookcentury1800, bookdecade1880, bookidcu3192403121, bookyear1882
