Light wave

“ The objection to the wave theory of light, that light moves in straight lines while sound waves can bend around an obstacle, is shown to be groundless, since we have seen that if the sound waves are sufficiently short they cast a sound shadow, while by devices which take into account the extreme minuteness of light waves their bending around obstacles may be readily observed. ”

“ In all that has gone before, we have confined ourselves to the consideration of the single set of light-waves originated by a single vibrating molecule, and to single-convex lenses, having surfaces of the proper curvature, to convert the convex spherical or plane wave-fronts into concave spherical wave-fronts; but how is it in reality?
We have seen that the light of the sun originates in clouds of precipitated carbon from the great upward currents of metallic vapors rising from its interior. ”

“ It will be remembered that in one of the first illustrations of wave motion light waves were compared with the waves along a cord, and it was stated that the vibrations which caused the phenomena of light are known to be vibrations of this character rather than of the character of sound waves. The sound waves consist of vibrations in the direction of the propagation of the sound itself. The motion of the particles in the light waves are at right angles to their direction of propagation. ”

“ Modern science recognises that in the radiation from all bodies which give us white light there is so great a difference of length of wave in the vibrations that different effects are produced on different bodies. ”

“ According to this picture, the energy of a light wave emitted from a point source is not spread continuously over ever larger volumes, but consists of a finite number of energy quanta that are spatially localized at points of space, move without dividing and are absorbed or generated only as a whole. ”

“ The physical effect we call light, and that which we have up to the present moment merely called electric radiation, are really identical in nature, and both consist in waves propagated through the space-filling æther, the only difference between them is in wave-length and wave-amplitude. ”

“ Accordingly, the experiment of producing interference between two sets of light rays so that they destroy each other is a strong argument in favour of the view that light must consist in some kind of wave-motion existing in a medium susceptible of supporting it, filling all space, and existing in all transparent bodies. ”

“ Every substance to be examined must first be made to glow, made luminous; and as nearly everything in the heavens is luminous the instrument has a great range in Astronomy. And when we speak of analysing light, we mean that [Pg 22] the light may be broken up into waves of different lengths. What we call light is a series of minute waves in ether, and these waves are—measuring them from crest to crest, so to say—of various lengths. Each wave-length corresponds to a colour of the rainbow. The shortest waves give us a sensation of violet colour, and the largest waves cause a sensation of red. ”

“ Two bright lights may be made to produce darkness.—If two pencils of light radiate from two spots very close to each other in such a manner that they cross each other at a given point, any object placed at that line of interference will be illuminated with the sum of the two luminous pencils. If we suppose those rays to move in waves, and the elevation of the wave to represent the maximum of luminous effect, then the two waves meeting, when they are both at the height of their undulation, will necessarily produce a spot of greater intensity. ”

“ If light of one wave length is used, as red light, the regions of reinforcement and interference are shown by red and dark rings, while if white light is used, the ring where red light interferes, yields its complementary color, greenish blue. ”

“ The answer of the wave theory to the objection now is, that light does bend round corners though only slightly and that the smallness of the bend is quite simply due to the extreme shortness of the light waves. The longer waves are, the more they bend round corners. ”

“ When light is scattered by particles which are very small compared with any of the wave-lengths, the ratio of the amplitudes of the vibrations of the scattered and incident light varies inversely as the square of the wave-length, and the intensity of the lights themselves as the inverse fourth power. ”

“ If light is a substance, no possible explanation can be given which will enable us to account for the combination of two rays of light producing darkness at their meeting-point. If, on the other hand, rays of light consist of waves of some kind in a medium, then, as we have seen in the case of water ripples and air waves, it is quite possible for two wave-trains to annihilate each other’s effect at a certain point, if a hollow of one wave-train reaches [191] that place coincidently with a hump belonging to the other. ”

“ DOES THE SPEED OF LIGHT IN SPACE DEPEND UPON ITS WAVE-LENGTH?
When a beam of light comes through a prism of glass or a raindrop it is dispersed into a band of vivid colors, each denoting a particular wave-length. Though all these wave-lengths travel together in the air they part company in the glass or the water because there they no longer possess the same speed. The long waves, which produce the sensation of red, travel faster than the short, or violet waves. ”

“ Light, on the other hand, appears to consist entirely in the movement of points of force transversely to the direction of propagation of the ray. The light-wave is partially analogous to the bending of a rod or of a stretched cord agitated at one end. ”

“ By causing the light to pass through a prism the mixed rays are sorted out side by side according to their several wave-lengths, forming a [Pg 12] broad, many-hued band or “spectrum” upon a white screen placed to receive it. (See Fig. 1.) To the visible rays of the longest wave-length is due the red colour on the extreme left. Waves of somewhat shorter length produce the adjoining stripe of orange, and the succeeding colours—yellow, green, and blue—correspond respectively to waves of shorter and shorter lengths. ”

“ The oldest valid and conclusive requisition of an ethereous medium depends on the wave theory of light, one of the founders of which was the Royal Institution Professor of Natural Philosophy at the beginning of last century, Dr. Thomas Young.
No ordinary matter is capable of transmitting the undulations or tremors that we call light. The speed at which they go, the kind of undulation, and the facility with which they go through vacuum, forbid this. ”

“ The light .of the firmament comes to us across the direction of the solar rays, and even against the direction of the solar rays; and this lateral and opposing rush of wave-motion can only be due to the rebound of the waves from the air itself, or from something suspended in the air. It is also evident that, unlike the action of clouds, the solar light is not reflected by the sky in the proportions which produce white. ”

“ The waves generated in the ether by the swinging atoms of luminous bodies are of different lengths and amplitudes. The amplitude is the width of swing of the individual particles of the wave. In water-waves it is the height of the crest above the trough, while the length of the wave is the distance between two consecutive crests. The aggregate of waves emitted by the sun may be broadly divided into two classes: the one class competent, the other incompetent, to excite vision. But the light-producing waves differ markedly among themselves in size, form, and force. ”

“ Light propagates through space as a wave. The amplitudes, wavelengths, frequencies, and speed of light are affected by how light is emitted and the particular conditions of the material through which it is propagating. ScienceApologist (talk) 20:23, 20 April 2009 (UTC) The frequency of light waves is determined by the period of the oscillations of the emitter. While the frequency of a light wave does not normally change as light travels through different materials, called optical media, the wavelength of light is affected by the indexes of refraction in different media. ”

“ LIGHTING. Artificial light is generally produced by raising some body to a high temperature. If the temperature of a solid body be greater than that of surrounding bodies it parts with some of its energy in the form of radiation. Whilst the temperature is low these radiations are not of a kind to which the eye is sensitive; they are exclusively radiations less refrangible and of greater wave-length than red light, and may be called infra-red. As the temperature is increased the infra-red radiations increase, but presently there are added radiations which the eye perceives as red light. ”

“ Light, the stimulus, is physically a wave motion, its vibrations succeeding each other at the rate of 500,000000,000000 vibrations, more or less, per second, and moving through space with a speed of 186,000 miles per second. The "wave-length", or distance from the crest of one wave to the crest of the next following, is measured in millionths of a millimeter.
The most important single step ever taken towards a knowledge of the physics of light, and incidentally towards a knowledge of visual sensations, was Newton's analysis of white light into the spectrum. ”

“ When light is analysed by a prism or grating into a spectrum, the course of each ray is deflected—refracted or diffracted—by an amount corresponding to its frequency of vibration or wave-length.
Motion of the medium, so long as it is steady, affects neither frequency nor wave-length, and accordingly is without influence on the result. ”

“ Thus the rate of transmission of light waves is different for air, glass, water, and other substances through which they may pass and such bodies as are entirely opaque are supposed to suppress the ether vibrations, resulting in light entirely. ”

“ A wave of a certain velocity and length gives us a certain sensation which we call blue; another awakens the sensation we call yellow. The two series of waves, mingling, produce a new sensation which we call green. The necessity of reflection for the production of these sensations is evident. The mingled waves have no color in their incident flow; but, striking some object, these waves become separated, some being absorbed, and the reflected ones produce the peculiar sensation we call color.
We know that these varying conditions of light which affect us as color have an absolute being. ”

“ Light is transmitted by waves, similar in some ways to waves in water, the light waves being disturbances of the light-bearing ether, an invisible, imponderable substance of zero density and infinite elasticity, which pervades all matter. ”

“ I shall show the distinction between these vibrations and the vibrations of light. Here is the fixed appearance of the particles when displaced but not in motion. You can imagine particles of something, the thing whose motion constitutes light. This thing we call the luminiferous ether. That is the only substance we are confident of in dynamics. One thing we are sure of, and that is the reality and substantiality of the luminiferous ether. This instrument is merely a method of giving motion to a diagram designed for the purpose of illustrating wave motion of light. ”

“ Emission Theory supported by Newton, opposed by Huyghens; the Wave Theory established by Young and Fresnel; Theory explained; nature of Sound; of Music; of Pitch; nature of Light; of Colour; two sounds may produce silence; two rays of light may produce darkness; two rays of heat may produce cold; Length and Number of waves of light; Liquid Waves; Interference; Diffraction; Colours of Thin Plates; applications of the foregoing to cloud iridescences, luminous trees, twinkling of stars, the Spirit of the Brocken, &c.
2.—Radiant Heat. 239
The Sun emits a multitude of Non-luminous Rays ”

“ The phenomena of the interference of beams of light in certain circumstances, to produce darkness or colour, indicate that light is some form of wave motion, and, to carry these waves, a hypothetical luminiferous aether was invented. ”

“ One of the simplest proofs is found in the common lens or burning-glass, by which the light waves are brought to a focus, and as a result, heat is manifested. Although there is this close identity between light and heat waves, yet there must be some distinction between the heat and light waves, because while light waves affect the eye, heat waves do not. ”

“ A beam of white light is formed by the union of innumerable different waves whose lengths have almost every possible value lying between certain limits. The wave-length of red light is such that there are 33,000 waves in an inch, while that of violet light is but little more than half that of red light. ”

“ We may note, in passing, that it is not every transparent body when fashioned into a prism which thus analyzes the light into a fan-shaped beam with rays of various wave-lengths arranged in the order of their wave-lengths. ”

“ Thirdly, they are of such a nature, as does either more easily or more difficultly transmit the Rays of light then the liquor; if more easily, a Blue is generated, and if more difficultly, a Red or Scarlet.
And first, let us suppose the tinging particles to be of a substance that does more impede the Rays of light, we shall find that the pulse or wave of light mov'd from A D to B C, will proceed on, through the containing medium by the pulses or waves K K, L L, M M, N N, O O ”

“ Optics has nevertheless certain distinctly speculative features. Wave-motion demands a medium. The enormous velocity of light excludes known forms of matter; the transmission of radiation in vacuo and through outer space from the most remote regions of the universe, and at the same time through solids such as glass demands that this medium shall have properties very different from that of any substance with which chemistry has made us acquainted. ”