Photon

“ This stuff should be able, with the aid of a molecular motion beam, which will make all the photons move in parallel paths, to move at the full speed of each photon—186,000 miles a second. The [Pg. 198] tremendous speed of these individual photons is what makes the material so hard. Their kinetic impulse is rather considerable! It's the kinetic blow that the molecules of a metal give that keeps other metal from penetrating it. ”

“ After a thousand thousand years, and billions on billions of such repetitions, the handful of photons reached the relatively cool photosphere of the sun. But the long battle had taken some of the drive out of them; over the past million years, even the strongest had become only hard ultraviolet, and the weakest just sputtered out in the form of long radio waves. ”

“ Later, using spectroscopy, which is a technique used in every natural science, they compare the colors missing with the ones that atoms emit.
The light of the stars interacts with electrons within atoms. Photons with the exact energy are absorbed and drive electrons to higher energy levels. ”

“ Classical electromagnetism isn't so much an assumption as it is a framework. OK, I'm making the change I suggested. "Quantum optics deals with the best model of light scientists have developed to date: the photon." I really like this sentence: it reminds us that science may progress further and develop yet better models. psychology?? I hope it explains later in the article how this is related. Optical illusions. Ah! emission theory: Instead of the wikilink to wikipedia:Emission theory perhaps what you want is to link to wikipedia:Emission theory (vision) . ”

“ Why does the color of light, and not its intensity, determine whether a certain photochemical reaction occurs? Why is light of short wavelength generally more effective chemically than light of longer wavelength? Why is the speed of photoelectrically produced cathode rays independent of the light's intensity? Why are higher temperatures (and, thus, higher molecular energies) required to add a short-wavelength component to the radiation emitted by an object?
The oscillation theory, in its present formulation, gives no answers to these questions. ”

“ We now come to another very important discovery, made by means of our prism and narrow slit—the determination of the composition of the photosphere or mass of luminous vapour surrounding the body of the sun.
A simple experiment will show how this brilliant discovery was arrived at. The light of a candle or other flame containing incandescent solid matter is passed through the spectroscope, and is found to decompose into a continuous spectrum, uninterrupted by dark lines. Between the light and the slit a spirit-lamp is placed, but no difference in the appearance of the spectrum is perceived. ”

“ They are: 'optical refraction', 'light-ray', and 'light-velocity' - the latter two serving to explain the first. In a science of optics which seeks its foundation in the intercourse between man's own visual activity and the doings and sufferings of light, these three concepts must needs undergo a decisive change, both in their meaning and in their value for the description of the relevant optical phenomena. For they are all purely kinematic concepts typical of the onlooker-way of conceiving things - concepts, that is, to which nothing corresponds in the realm of the actual phenomena. ”

“ Lenses—The image cast by a convex lens—Focus—Relative position of object and lens—Correction of lenses for colour—Spherical aberration—Distortion of image—The human eye—The use of spectacles—The blind spot.
Light is a third form of that energy of which we have already treated two manifestations—heat and electricity. The distinguishing characteristic of ether light-waves is their extreme rapidity of vibration, which has been calculated to range from 700 billion movements per second for violet rays to 400 billion for red rays. ”

“ The research-field of optics includes the investigation of the rays which we have just enumerated. A delimitation may then be made, inasmuch as luminous sources yield no other radiations, and also since the next series of waves, the electromagnetic waves, have a minimum wave-length of 6 mm.
§ 2. The commonest subjective phenomena of light are colour and visibility, i.e. why are some bodies visible and others not, or, in other words, what is the physical significance of the words “transparency,” “colour” and “visibility.” ”

“ Among the most important of these modern instruments are the telescope, the spectroscope, and the photographic camera; and since all these instruments deal with the light which comes from the stars to the earth, we must for their proper understanding take account of the nature of that light, or, more strictly speaking, we must take account of the radiant energy emitted by the sun and stars, which energy, coming from the sun, is translated by our nerves into the two different sensations of light and heat. ”

“ Reflection of light is essential to the visual perception of substances. We could not see a substance if it did not reflect light—unless it is warm enough to emit radiation in the visible wavelengths. Selective reflection of light wavelengths determines the apparent color of a substance; a substance has a certain color because that wavelength is being reflected and the others absorbed. ”

“ 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. ”

“ 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. ”

“ The light waves will forever prevent us from actually seeing the atom. But I have perfected a system of photography which magnifies particles smaller than light waves, and, separating their images from the light waves, renders detail clear in the moving pictures. ”

“ It is hardly necessary to occupy time with experiments in showing that a ray of light can be reflected and refracted by mirrors and prisms, and converged or diverged by transparent lenses. These are simple optical facts, and if you are not familiar with them it will be easy for you to make their acquaintance by studying any simple book upon optics; but I should like to draw your attention to the fact that, in addition to rays of light and electric radiation, we are acquainted with another kind of radiation, which is also susceptible of being refracted, and that is commonly called dark heat. ”

“ In the science of optics, as is well known, the phenomena of light are explained by the assumption that the energy is transmitted in waves through a medium which fills all space, called the luminiferous ether, and there is no question that this theory of Nature, known in science as the Undulatory Theory of Light, is, as a working hypothesis, one of the most comprehensive and searching which the human mind has ever framed. ”

“ Visible radiation × visual sensibility is spoken of as luminosity; (3) by the amount of light (expressed in candles) produced in relation to a given expenditure of energy or in relation to the cost of the energy expended. Thus, of the radiation emitted from an incandescent electric lamp only a small per cent. is light, the rest being heat and actinic rays. It is therefore very far from being 100 per cent. efficient. If there were no infra-red or ultra-violet in the radiation from an incandescent lamp its efficiency would be 100 per cent. if we disregarded visual sensibility. ”

“ Can anything appeal more to the imagination than the fact that we can detect the peculiarities in the internal molecular structure of an opaque body by means of light that is itself invisible? Could anything have been more unexpected than to find that a sphere of China-clay focuses invisible light more perfectly than a sphere of glass focuses the visible; that in fact, the refractive power of this clay to electric radiation is at least as great as that of the most costly diamond to light? ”

“ Again, if we have an extremely complex light-source, let us say a solid and a mixture of gases giving us light, and we allow the light to enter, so to speak, indiscriminately into the spectroscope, then in each part of the spectrum we shall get a summation—a complex record—of the light of the same wave-length proceeding from all the different light-waves. But if by means of a lens we form an image of the light source, so that each particular part shall be impressed in its proper place on the slit-plate, then in the spectrum the different kinds of light will be sorted out. ”

“ Ordinary light passes through transparent bodies without producing any very striking effects in its passage; but this extraordinary beam of light has the power of insinuating itself between the molecules of bodies, and by illuminating them, and giving them every variety of prismatic hue, of enabling the eye to detect something of the structure of the mass. The chromatic phenomena of polarized light are so striking, that no description can convey an adequate idea of their character. ”

“ If each energy quantum of the exciting light releases its energy independently from all others to the electrons, the distribution of velocities of the electrons, which means the quality of the generated cathode radiation, will be independent of the intensity of the exciting light; the number of electrons that exits the body, on the other hand, will, in otherwise equal circumstances, be proportional to the intensity of the exciting light. ”

“ Hence it is that if we examine the light of a match or candle, or even the electric light, we get such a continuous spectrum, because these light sources emit rays of every refrangibility. Modern science teaches us that they do so because the molecules—the vibrations of which produce, through the intermediary of the ether, 402the sensation of light on our optic nerve—are of a certain complexity. ”

“ The trouble is we need one that transmits the visible portion of the spectrum and—boy—that's it, Wright, that's it—spectrum—take a totally reflecting diffraction grating, reflect out all that part of the spectrum that we don't want, take what we do, pass it through a prism to recombine it to white light, then through lenses so we can see as if through a telescope! ”

“ When we make a telescope with a lens we use a property of light called refraction, a word from the Latin which means simply breaking back. You know how a cricket ball can be bowled so as to go straight for some distance, and then when it hits the surface of the ground it "breaks back" owing to the spin the bowler has given it? Well, a beam of light behaves in much the same way when it is refracted; after going straight for some distance, it strikes a surface and turns off at an angle. ”

“ To study the phenomena of diffraction it is necessary that our source of light should be a physical point, or a fine line; for when a luminous surface is employed, the waves issuing from different points of the surface obscure and neutralize each other. A point of light of high intensity is obtained by admitting the parallel rays of the sun through an aperture in a window-shutter, and concentrating the beam by a lens of short focus. The small solar image at the focus constitutes a suitable point of light. ”

“ Some substances have the property of transforming luminous radiations, presenting the phenomena of Calorescence, Fluorescence and Phosphorescence. An optical system is composed of any number of Mirrors or Lenses, or of both. If light falling on a system be not brought to a focus, i.e. if all the emergent rays be not concurrent, we are presented with a Caustic and an Aberration. An optical instrument is simply the setting up of an optical system, the Telescope, Microscope, Objective, optical Lantern, Camera Lucida, Camera Obscura and the Kaleidoscope are examples ”

“ The sun consists of a nucleus surrounded by a flaming atmosphere. The light of the nucleus would give us a continuous spectrum, like that of our common carbon-points; but having to pass through the photosphere, as our beam had to pass through the flame, those rays of the nucleus which the photosphere can itself emit are absorbed, and shaded spaces, corresponding to the particular rays absorbed, occur in the spectrum. ”

“ A searchlight, of course, gives off heat. If we place a lens of the same size as the searchlight aperture in the path of the beam and concentrate all the light, and heat, at one spot, the focal point of the lens, the temperature at that point is the same as the temperature of the source of the light, less what has been lost by radiation. You understand that, do you not?”
“Certainly.”
“Suppose that we place at the center of the aperture of the searchlight a small opaque disc which is permeable neither to heat nor light, in such a manner as to interrupt the central portion of the beam. ”

“ To the unit of energy might be immediately attached other units. For instance, radiation being nothing but a flux of energy, we could, in order to establish photometric units, divide the normal spectrum into bands of a given width, and measure the power of each for the unit of radiating surface. ”

“ B. The same effect in concentrating the rays, is produced by the refraction with a lens, as by the reflection from a concave mirror: in the first, the rays pass through the glass and converge to a focus, behind it, in the latter, they are reflected from the mirror, and brought to a focus, before it. A lens, when used for the purpose of collecting the sun's rays, is called a burning glass. I have before explained to you, the manner in which a convex lens, refracts the rays, and brings them to a focus ”