POLARIZATION* OP LIGHT. 



POLARIZED RINGS. 



-lump. We are driven to conceive that a sliding motion 

 the ether, layer orer layer, U misted by a tangential force thereby 

 called into play : in fact, to treat the ether, 10 far a the vibration* of 

 light are concerned, u if it were an elastic solid. Still, it would ill 

 acoord with the apirit of inductive philosophy to reject a conclusion to 

 which we are fairly led by the study of observed phenomena, because 

 it clashes with preconceived notion* respecting the nature of a 

 medium of the very existence of which we have no evidence beyond 

 the beautiful and simple explanation it aflbrdi of the curious and com- 

 plicated phenomena of light. 



If once we adopt the theory of transversal vibrations, we are able not 

 only to form a clear picture in the mind of what, to Bay the least, 

 polarization nay be, but to explain in the simplest manner both 

 Malua'a law and the laws of interference of polarized light. In fact. 

 Malm's law and laws 2, 4, 5, of interference led to the theory of trans- 

 venal vibration* ; and to explain these law* on the theory we have 

 only to begin at the other end. Laws 1 and 3, which assert the neces- 

 sity of a polarizer in order that any colours should be seen in crystal- 

 line platen, follow at once from the consideration that the rectangular 

 components of the vibrations in common light have no fixed and 

 permanent relation to each other, either as to phase or amplitude, so 

 that they are at good at the vibrations belonging to two streams from 

 different source*. 



The theory of transversal vibrations, again, enables us to form a 

 perfectly clear notion of the nature of a peculiar modification of light, 

 known as elliptic polarization. When polarized light is transmitted 

 across a crystalline plate, the emergent light is in general elliptically 

 polarized, being only in particular cases polarized in the way 

 hitherto considered in this article, or jilant-pnlarized, as it is 

 railed in contradistinction to elliptic polarization. When ellip- 

 tically polarized light U examined by an analyzer which is made 

 to revolve, the light never wholly vanishes, but becomes alternately 

 a maximum and a minimum at every quarter revolution. Thus 

 far it agrees with partially polarized light, from which, however, it 



wholly differs in other respects, both theoretically and experimentally. 

 [KII.IITIC POLARIZATION.) 



Lastly, the theory of transversal vibrations U, to say the least, very 

 hopeful in its application to the explanation of double refraction, of 

 the polarization of light by reflection, Ac. The full explanation of 

 these phenomena U retarded by two cause*, first, there are tin- Inlim-nt 

 mathematical difficulties of the problem, and secondly, which is far 

 worse, in our ignorance of the ultimate constitution of matter, and its 

 relation to the luminiferou* ether, we have to grope in the dark in our 

 endeavour to find out what is the real state of things to which our 

 mathematics have to be applied. Still, even in this department many 

 important laws have already been explained, and frequently even pre- 

 dicted, on dynamical principles, though not always with perfect 

 rigour ; but no dynamical theory has yet accumulated in its favour 

 such a weight of evidence as to exclude others, nor can even the 

 question whether the vibrations of polarized light are parallel or per- 

 pendicular to the plane of polarization be yet considered settled, though 

 the probability seems to be in favour of the latter view, which was 

 that originally adopted by Presnel. 



In this article the subject of double refraction has not been touched 

 except so far as was necessary for the explanation of polarization. For 

 further information on this point see a subsequent article, UNIT i A 

 TORT THEORY. 



POLARIZATION, MOVEABLE. This term refers to an ingenious 

 theory by which M. Biot attempted to explain the colours of crystal- 

 line plates in polarized light. The theory is, however, liable to some 

 formidable objections ; and as the phenomena have since been 

 explained in the most simple and complete manner on the theory of 

 undulations [POLARIZATION! the reader who wishes for further infor- 

 mation on this subject is referred to M. Biot's original paper in the 

 1 3th volume of the ' Mdmoires de I'lnsti t ut.' 



POLARIZED RINGS. The beautiful coloured rings or curves seen 

 with polarized light about the optic axis or axes of doubly refracting 

 crystals. [UNDDLATORY THEORY.] 



