Polarized light

“ Elliptically polarized light is investigated by the reduction of the pencil to a state of plane polarization, and a determination of the resulting plane of polarization. One method consists in finding directly the elliptic constants of the vibration by means of a quarter wave plate and an analyser; but the more usual plan is to measure the relative retardation of two rectangular components of the stream by a Babinet's compensator. ”

“ Hence, as in the light case, we may call A a polarizer of vibrations, and B an analyzer.
Fig. 55.
Now if polarized light is passing from A to B (Fig. 54) through the air, say, and we have the analyzer placed so that there is darkness, we find that if we place in the path of the ray some solution of sugar we shall no longer have darkness at B; we must turn B round to get things dark again; this is evidence of the sugar solution having twisted round the plane of polarization of the light. ”

“ In order to account for certain phenomena in optics, philosophers have assumed that rays possess polarity; and polarized light is light which has had the property of Polarization conferred upon it by reflection, refraction, or absorption. ”

“ Whenever the particles of the foreign matter are sufficiently fine, the light emitted laterally is blue in colour, and, in a direction perpendicular to that of the incident beam, is completely polarized. ”

“ Light is also polarized by reflection from the surface of a transparent medium. When a ray of ordinary light falls on a plate of glass at an angle of 54° 55 ́ with the normal, the reflected ray is perfectly polarized, and at other inclinations the polarization is incomplete. Here then is polarization by reflection. Fig. 207 shows an apparatus for producing this phenomenon. The light foiling on the first mirror from E is reflected through the tube as a polarized beam, and this is analyzed by the other mirror (I) , whose plane can be rotated round the axis of the tube. ”

“ When the ray of polarized light reflected from the first set of glass plates enters the doubly refracting film of selenite, which is about the fortieth or fiftieth part of an inch in thickness, it is split into the ordinary and extraordinary rays, and is said to be dipolarized, and forms two planes of polarized light, vibrating at right angles to each other. ”

“ Although all reflected light does not reach us as polarized light, yet I think the small percentage of polarization, taken with the faintness of the dark lines, indicates that the corona is, to a considerable extent, self-luminous. ”

“ I am afraid I am worrying you with rather hard notions this afternoon, or at any rate hard names; there is nothing very hard about the notion of polarized light, if you will think of a ray of light as a flat thing like a strip of cardboard which will bend quite easily sideways but not edgeways. ”

“ Light is polarized by transmission and by reflection. We have already, when we were discussing the principle involved in the double-image micrometer, seen how a crystal of Iceland spar divides a ray into two parts at the point of incidence. Now these two rays are oppositely polarized, that is to say, the vibrations take place in planes perpendicular to each other; the vibrations of the incident light in one plane are refracted more than the vibrations in the opposite plane, and we have therefore two rays, one called the ordinary ray, and the other the extraordinary ray. Fig. ”

“ If the mode of observation which we have applied to smooth glass plates be universally employed, it may serve to show that polarization when complete is always a modification exactly of the same kind, for all substances: for when a beam of light has been once polarized, it will equally pass through all substances, with the exception mentioned above, provided each be presented to it under its proper angle, and whatever be the nature of the first or second substance employed, the variation of intensity in the light after the second reflexion is always subject to the same laws. ”

“ Light is called polarized, which, having been once reflected or refracted, is incapable of being again reflected or refracted in certain positions of the second medium. Ordinarily, light which has been reflected from a pane of glass or any other substance, may be a second time reflected from another surface, and will also freely pass through transparent bodies. ”

“ It is not only crystalline bodies that modify polarization impressed on the rays of light: Messrs. Malus and Biot found by different experiments made about the same time, that if a ray be refracted successively by several glass plates placed parallel to each other, it will at length be polarized in one single direction perpendicular to the plane of refraction. ”

“ If the primary ray is unpolarized, the light scattered north and south is entirely due to that component which vibrates east and west, and is therefore perfectly polarized, the direction of its vibration being also east and west. ”

“ Having thus determined the fact of polarization, the next step was to ascertain what percentage of the light is polarized. For this purpose, the author again had to devise novel apparatus. The amount of polarization was determined to be, "with a high degree of probability, as much as 15 per cent., but can hardly be as much as 20 per cent."
The fact of polarization implies that the light is reflected, either wholly or in part, and is thus derived originally from the sun. The spectrum of the zodiacal light is not perceptibly different from that of sunlight, except in intensity. ”

“ It's fine now. (except maybe for Faraday) ☺Coppertwig (talk) 01:37, 23 May 2009 (UTC) Please explain why scattering in the atmosphere would cause polarization. What's asymmetric? Oh, wait, I get it: it's the scattered light that's polarized. I changed the wording so it sounds more as if it's talking about the scattered light, rather than the light that is continuing to pass through the atmosphere in its original direction. You got it. The first paragraph of Modern Optics almost makes me feel like starting a new career in one of those fields! ”

“ Similarly any other ray scattered horizontally is perfectly polarized, and the vibration is performed in the hori- zontal plane. In other directions the polarization becomes less and less complete as we approach the vertical.
The observed facts as to polarization are thus readily explained,
and the general law connecting the intensity of the scattered light with the wave-length follows almost as easily from con- siderations of dimensions. ”

“ The polarization of the light transmitted by the pile is never complete, but tends to become more nearly so as the number of the plates is increased and at the same time the angle of incidence for which the polarization is a maximum approaches indefinitely the polarizing angle (Sir G. G. Stokes, Math. and Phys. Papers, iv 145) .
In order to isolate a polarized pencil of rays with a rhomb of Iceland spar, it is necessary to have a crystal of such a thickness that the emergent streams are separated, so that one may be stopped by a screen. ”

“ An extreme case is that of the unpolarized light emitted by incandescent solid bodies, consisting of disturbances whose variations are highly irregular, and giving a continuous spectrum. But even with what is commonly called homogeneous light, no perfectly sharp line will be seen. ”

“ About noon, as nearly as we could guess, our attention was again arrested by the appearance of the sun. It gave out no light, properly so called, but a dull and sullen glow without reflection, as if all its rays were polarized. Just before sinking within the turgid sea, its central fires suddenly went out, as if hurriedly extinguished by some unaccountable power. It was a dim, sliver-like rim, alone, as it rushed down the unfathomable ocean. ”

“ On looking at the sun in the polariscope, the image, as before observed, is seen to be purely white—a proof that the medium through which the luminous substance is made visible to us is gaseous. If it were liquid, the light would be coloured; and as regards solidity, that is out of the question—the rapid change of spots proves that the outer envelope of the sun is not solid. On whatever day of the year we examine, the light is always white. Thus, these experiments remove the theory out of the region of simple hypothesis, and give certainty to our conclusions respecting the photosphere. ”

“ Consequently two kinds of light were given off by this star; one forming a series of bright lines indicative of luminous gas, the other consisting of a continuous spectrum, crossed by dark lines, showing the existence of a solid body in a state of incandescence, surrounded by a photosphere of luminous vapours. Two of the bright lines undoubtedly showed the presence of hydrogen in a state of illumination, the great brightness of the lines indicating that the burning gas was hotter than the photosphere. ”

“ At the blue pole, the lightness-effect springs from the resistant medium through which we gaze, a medium under the influence of gravity, while the darkness is provided by the anti-gravity quality of cosmic space, which as a 'negative' resistance exercises a suction on the eye's inner light. At the yellow pole it is just the reverse. Here, the resistant medium brings about a darkening of our field of vision, while the lightness-effect springs from a direct meeting of the eye with light, and so with the suctional effect of negative density. ”

“ Availing themselves, therefore, of the assistance of polarised light, and an instrument named the polariscope, or polarising telescope, observers obtain a double image of the sun, both alike, and both white; but on reflecting this image on water, or a glass mirror, the rays become polarised; the two images are no longer alike or white, but are intensely coloured, while their form remains unchanged. If one is red, the other is green, or yellow and violet, always producing what are called the complementary colours. ”