Electricity for public schools and colleges . ular currentshas been revived as a somewhat fruitful view. § 16. Rotation of the Plane of Polarisation in a MagneticField.—In giving some account of certain phenomena that showa remarkable connection between magnetic and electric stresses onthe one hand, and radiant energy on the other, we must assumethat the reader has some acquaintance with the elements ofphysical optics. If this is not the case he is advised to readenough of the subject to understand (i.) what is meant by a ray oflight or of other radiant energy ; (ii.) what is meant by a planep
Electricity for public schools and colleges . ular currentshas been revived as a somewhat fruitful view. § 16. Rotation of the Plane of Polarisation in a MagneticField.—In giving some account of certain phenomena that showa remarkable connection between magnetic and electric stresses onthe one hand, and radiant energy on the other, we must assumethat the reader has some acquaintance with the elements ofphysical optics. If this is not the case he is advised to readenough of the subject to understand (i.) what is meant by a ray oflight or of other radiant energy ; (ii.) what is meant by a planepolarised ray, and by the plane of polarisation ; (iii.) what a Nicolsprism is, and how it is used to obtain a plane polarised ray; (iv.)how a second Nicols prism can be used as an analyser to detectwhether a ray is plane polarised, and whether the plane of polarisa-tion has been rotated or has changed its azimuth. Now it is found that if a plane polarised ray be passed througha transparent medium that ordinarily has no power to rotate the. Fig. i. plane, and if this medium be placed in a powerful magnetic field,then the plane of polarisation of the ray is in general slightlyrotated in its passage through the medium. It was Faraday whodiscovered this. The accompanying figure indicates how the z 338 ELECTRICITY ch. xs. electro-magnetic rotation of a plane polarised ray may be de-monstrated. If more exact results are desired the necessaryexperimental arrangements are less simple. M and N are powerfulelectro-magnels, provided with hollow iron cores, their unlike polesbeing opposed so as to give a powerful field at c. Here is placedthe piece of glass or other transparent body, whose rotating powers,when subject to a powerful magnetic field, are to be observed. Atb is ihe polarising Nicol, and at a the analyser. If (as we here suppose) the body at c has no innate rotatingpower as has {) quartz, then before the current passes the planeof polarisation of the ray is not rotated ;
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Keywords: ., bookcentury1800, bookdecade1890, bookpubl, booksubjectelectricity
