Mr. R. Moon on Polarization and Double Refraction. 35S 



vals. On the present occasion I shall endeavour to point out 

 a consequence of the latter part of this hypothesis which has 

 recently suggested itself to me. 



Dr. Young, in his Theory of Reflexion, takes for granted 

 that the waves composing common light occur in uninterrupted 

 succession. Rut if we make a careful application of the pro- 

 cess of reasoning which he has adopted to the case in which the 

 waves are supposed to occur at finite intervals, we shall find 

 that if a series of such waves be reflected at a plane surface, 

 the reflected light will not consist of continuous waves, but 

 the surface of each reflected wave will be intersected by dark 

 bands, in which there will be no vibration. These bands will 

 be parallel to each other and to the intersection of the inci- 

 dent waves with the reflecting surface, and their breadth will 

 at first be exactly equal to the interval between two waves of 

 the incident light. We say at first, for after reflection the 

 broken surface of the wave will tend to re-unite so as to form 

 a continuous surface, though this continuity will never be 

 perfectly effected, so that the reflected waves will always con- 

 sist of parallel bands of varying intensity. If the light be 

 again reflected in a plane perpendicular to the plane of first 

 reflexion, we shall, in like manner, have the surface of the 

 waves twice reflected, intersected by two series of bands per- 

 pendicular to each other. Hence it is plain that if the inter- 

 vals between the waves of the incident light bear any consi- 

 derable proportion to the breadth of the waves, very little 

 light will be transmitted after the second reflexion ; and the 

 light so transmitted will be different in character, both from 

 common light and from light only once reflected ; the waves 

 being discontinuous in every direction, may not this disconti- 

 nuity be such as to prevent vision ? and is it not possible that 

 the change in the nature of the reflected waves which we have 

 endeavoured to point out may constitute polarization ? 



If we address ourselves to the case of refraction, we shall 

 be led to similar results. But it should be observed that, as 

 in the case of refraction, the breadth of the bands will not be 

 equal to the interval between two waves, but will be equal to 



~. — r multiplied into that interval. Hence we see that in the 

 smt 



case of refraction the discontinuity of the wave will be sooner 

 repaired than in the case of reflexion, or the polarization will be 

 less -perfect. The case of double refraction presents great, if 

 not insuperable, difficulties, but these we will not altogether 

 despair of removing. It will be observed that the polarization 

 of which we have spoken must always take place in a plane per- 

 pendicular to the intersection of the incident waves with the 



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