The science of light . -venient stand, while themirror B is fixed at thesame angle, but on avertical axle which canbe rotated by a beltand a pulley, or by anyother convenient cylindrical ring ofparchment paper or ofsome other translucentmaterial surrounds therevolving plate and re-ceives the light reflectedfrom it. A bright source of light is placed in thedirection S so that a ray reflected from A falls verti-cally on B and is reflected by it on to the parchment,making a patch of light there. If B is turned so that itis parallel to A a fairly bright patch of light is seen onthe parchme
The science of light . -venient stand, while themirror B is fixed at thesame angle, but on avertical axle which canbe rotated by a beltand a pulley, or by anyother convenient cylindrical ring ofparchment paper or ofsome other translucentmaterial surrounds therevolving plate and re-ceives the light reflectedfrom it. A bright source of light is placed in thedirection S so that a ray reflected from A falls verti-cally on B and is reflected by it on to the parchment,making a patch of light there. If B is turned so that itis parallel to A a fairly bright patch of light is seen onthe parchment, showing that the light coming up to itis quite copiously reflected. If it is now turned through90° in either direction from this position the patch oflight disappears, and if turned through a further 90° itreappears as brightly as in the first position. In theintermediate positions the light is less copiously re-flected. If B is rapidly revolved we shall see a ring oflight on the parchment with two maxima and two. 78 THE SCIENCE OF LIGHT minima of brightness corresponding to the positions inwhich the light is most and least freely reflected. It isquite simple to imagine why light is polarised by re-flection, for it is quite conceivable that vibrationsparallel to the plane of the glass are less likely to pene-trate than those perpendicular to the of the parallel vibrations will thereforebe reflected, and more of the perpendicularones transmitted. Polarisation by Refraction. — We shouldtherefore expect the refracted beam to bepolarised as well, and this is found to be thecase. The refracted beam is only partiallypolarised, however. If we make it pass througha succession of plates all placed at the polaris-ing angle, each plate will reflect more of theparallel vibrations, so that after passing through anumber of plates the transmitted beam is practicallycompletely polarised in the perpendicular or ten plates of glass will almost completelypolaris
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Keywords: ., bookcentury1900, bookdecade1910, booksubjectlight, bookyear1910
