The London, Edinburgh and Dublin philosophical magazine and journal of science . ine in it at right angles to ON,0 Q is the direction of vibration forthe wave along ON; and it mayhappen, clearly, that 0 P and 0 Q areinclined to one another at a largeangle even when OM and ON areclose together. Suppose, then, that theextraordinary pencil of wave-normalswhich is traversing the spar is slightly conical, and that 0 N,0 M are two of the wave-normals ; the planes of polarizationare inclined to each other at an angle equal to P 0 Q ; and thismay be considerable. Or, again, suppose that we have apolar
The London, Edinburgh and Dublin philosophical magazine and journal of science . ine in it at right angles to ON,0 Q is the direction of vibration forthe wave along ON; and it mayhappen, clearly, that 0 P and 0 Q areinclined to one another at a largeangle even when OM and ON areclose together. Suppose, then, that theextraordinary pencil of wave-normalswhich is traversing the spar is slightly conical, and that 0 N,0 M are two of the wave-normals ; the planes of polarizationare inclined to each other at an angle equal to P 0 Q ; and thismay be considerable. Or, again, suppose that we have apolarized pencil of parallel wave-normals incident on theprism. We determine the position of their plane of polariza-tion by turning the prism until no light passes through. Sup-pose that, when this is the case, the incident light is parallel to0 M. Now let the plane of polarization of the incident lightbe rotated, and suppose we wish to measure this rotation ; weturn the prism until the light is again quenched. Theoreticallythe axis round which the prism has been turned should be. Polarizing Prisms. 355 parallel to 0 M. In practice it is difficult to ensure this; andin general the direction of the wave-normal relatively to theoptic axis will be changed, and may now be ON say. Butsince the planes of polarization of the waves along 0 M and0 N are different, the angle through which the prism has beenturned will not be the angle through which the plane of pola-rization of the incident light has moved. Now Nicols prism is so cut that the angle between theplanes of polarization of two waves inclined to each other atbut a small angle as they traverse the crystal is , then, a slightly conical pencil traverse the prism, the anglesbetween the planes of polarization of the different waves areconsiderable; or if a parallel pencil traverse the prism inclinedat but a small angle to the axis of rotation, and the plane ofpolarization of this beam be rotated, that rotation will diffe
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Keywords: ., bookcentury1800, bookdecade1840, booksubjectscience, bookyear1840
