Light beam

“ A light beam, A B, having two square inches of pith, C, at one end, is balanced on a very fine fibre of glass, D D', stretched horizontally in a tube; one end of the fibre being connected with a torsion handle, E, passing through the tube, and indicating angular movements on a graduated circle. The beam is cemented to the torsion fibre, and the whole is inclosed in glass, and connected with the mercury pump by a spiral tube, F, and exhausted as perfectly as possible. G is a spiral spring, to keep the fibre in a uniform state of tension, H is a piece of cocoon silk. ”

“ Scientists are experimenting with a new kind of “lens”, one that uses variations in the density of gases to focus and guide the beam automatically. Since there are no surfaces in the path of the light beam, and since the gas is transparent and free of turbulence, the laser beam is not appreciably weakened or scattered as it travels through the pipe. ”

“ For when the most refrangible Rays are by a total Reflexion taken out of the beam MO, and leave that beam of an orange Colour, the Excess of those Rays in the reflected Light, does not only make the violet, indigo and blue at p more full, but also makes the beam MN change from the yellowish Colour of the Sun's Light, to a pale white inclining to blue, and afterward recover its yellowish Colour again, so soon as all the rest of the transmitted Light MOT is reflected. ”

“ To thus examine the constituents of a beam of light a lantern, with a lime-light or electric light, may be used for throwing a constant beam; we may then produce an image of the cylinders of lime or the carbon points in the lantern on a piece of paper or a screen, and our eyes will tell us that this is an instance of how the radiations from any incandescent substance are competent to give us light. We receive all the rays to which our eyes are tuned and we see a white image on the screen. ”

“ In arranging the apparatus for the purpose of reproducing sound at a distance, any powerful source of light may be used, but we have experimented chiefly with sunlight. For this purpose a large beam is concentrated by means of a lens upon the diaphragm-mirror, and, after reflection, is again rendered parallel by means of another lens. The beam is received at a distant station upon a parabolic reflector, in the focus of which is placed a sensitive selenium-cell, connected in a local circuit with a battery and telephone. ”

“ The reflected beam follows the law of reflection while the transmitted beam is seen to be refracted, or to have its courses slightly changed in direction upon entering the water. If the mirror is turned so that the angle at which the light strikes the water is changed, the amount of refraction or change of course of the light is varied. When the light strikes the water perpendicularly there is no refraction. On the other hand, the greater the angle at which the light strikes the water the greater the bending. ”

“ The beam is focused, just like the light that passes through a camera lens. The photographic lens, using light rays, picks up a picture and reproduces it again on the plate—just the same as the Express Ray picks up an object and sets it down on the other side of the world. ”

“ Of course, light-production has increased enormously in efficiency in the past century, but without optical devices for gathering the light, the enormous beam intensity would not be obtained. For example, consider a small source of light possessing a luminous intensity of one candle in all directions. If all this light which is emitted in all directions is gathered and sent forth in a beam of small angle, say one thousandth of the total angle surrounding a point, the intensity of this beam would be 1000 candles. It is in this manner that the enormous beam intensities are built up. ”

“ Place a large lens—as large as the aperture—in the way, and focus the beam on yourself, and you will feel a heat equal to that of the arc light—about seven thousand degrees Fahrenheit—less what has radiated into the surrounding air.
"Now, get out of that focus, and place an opaque disk on the center of the searchlight aperture, and the beam will go forth with a dark center, like a hollow pipe of light and heat. And this dark center will have the temperature of the outer air, plus only what has radiated into it from the surrounding pipe. ”

“ When red or green sectors are employed they should invariably be reinforced by mirrors, azimuthal condensing prisms, or other means to raise the coloured beam to approximately the same intensity as the white light. ”

“ If we throw a beam of light on a grating which contains perhaps some 14,000 parallel lines in the space of one inch in width, the lines being ruled on a plane and bright metallic surface, and receive the reflected beam on a screen, the appearance that is presented is a white central spot, together with six or seven spectra of gradually diminishing brightness on each side of it, all except the first pair overlapping one another. ”

“ If, therefore, a beam that has been rendered conical by a converging lens be sent through the spar so that the central ray of the cone passes along the axis, this ray only will escape double refraction. Each of the others will be divided into an ordinary and an extraordinary ray, the one moving more slowly through the crystal than the other; the one, therefore, retarded with reference to the other. Here, then, we have the conditions for interference, when the waves are reduced by the analyzer to a common plane. ”

“ This intense heat they project in a parallel beam against any object they choose, by means of a polished parabolic mirror of unknown composition, much as the parabolic mirror of a lighthouse projects a beam of light. ”

“ The circular beam may be considered as built up of flat and very thin bands of light, parallel to the edges of the prism, and a simple ray would be formed by one of these flat bands; as the round opening would allow an indefinite number of such rays to enter, each would produce its own spectrum on the screen, and the actual image would be formed of a number of spectra overlapping each other. When the aperture by which the light is admitted consists merely of a narrow slit, or line, parallel to the edges of the prism, we obtain what is termed a pure spectrum. ”

“ The great principle of radiation, which affirms that all bodies absorb the same rays that they emit, is now a familiar one. When, for example, a beam of white light is sent through a yellow sodium-flame, produced by a copious supply of sodium-vapor, the yellow constituent of the white beam is stopped by the yellow flame, and, if the beam be subsequently analyzed by a prism, a black band is found in the place of the intercepted yellow band of the spectrum. ”

“ It is well known that a beam, or pencil, of light, as emitted from the sun, is not a simple body, but is capable of being divided into seven prismatic colors. The image which is formed by the refraction of the pencil, by means of a prism, is called a Spectrum, and clearly exhibits the compound nature of light. The refracted rays of the Spectrum may be collected and made to constitute a pencil of light again, which will be white, or colorless as before. ”

“ Everyone knows that when a lamp is lighted the luminous rays are diffused on every side, horizontally as well as vertically. In lighthouse operations the beam has to be thrown in a horizontal line only, while the light which is shed towards the top and bottom must be diverted, so that the proportion of waste luminosity may be reduced to the minimum. While the parabolic reflector achieved this end partially, it was far from being satisfactory, and Fresnel set to work to condense the whole of the rays into a horizontal beam. ”

“ As a good illustration of the importance of reflected light and its connexion with luminous bodies, a beam of light from the oxy-hydrogen lantern may be allowed to pass above the surface of a table, when it will be noticed that the latter is lighted up only when the beam is reflected downward by a sheet of white paper. ”

“ The synthesis of white light may be effected in three ways, all of which are worthy of attention: Here, in the first instance, we have a rich spectrum produced by the decomposition of the beam (from L, fig. 9) . One face of the prism (P) is protected by a diaphragm (not shown in the figure) , with a longitudinal slit, through which the beam passes into the prism. It emerges decomposed at the other side. I permit the colours to pass through a cylindrical lens (C) , which so squeezes them together as to produce upon the screen a sharply defined rectangular image of the longitudinal slit. ”

“ Give us the real dope on how you're going to do it.”
“Well, with what I picked up from the Lassans, I think I know. They know all about light and mechanics, but they're rotten chemists, and don't realize how good a thing they've got in lots of ways. Now look—if you throw a beam of radiations from a cathode tube into finely divided material you break up some of the atoms. Well, all we have to do is get an extra-powerful cathode tube, break up a lot of atoms, and then deliver the positive charges from them onto whatever we're going for. That would be your gravity beam.” ”

“ The approach of a finger to either extremity of the beam causes the luminous index to travel several inches, slowing repulsion. A piece of ice brought near causes the spot of light to travel as much in the opposite direction. In order to insure the luminous index coming accurately back to zero, extreme precautions must be taken to keep all extraneous radiation from acting on the torsion-balance. ”

“ 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. ”

“ The fundamental idea, on which rests the possibility of producing speech by the action of light, is the conception of what may be termed an undulatory beam of light in contradistinction to a merely intermittent one. By an undulatory beam of light, I mean a beam that shines continuously upon the selenium receiver, but the intensity of which upon that receiver is subject to rapid changes, corresponding to the changes in the vibratory movement of a particle of air during the transmission of a sound of definite quality through the atmosphere. ”

“ The focal point is the theoretical centre of the luminous source, and the rays, coming from the top, sides, and bottom of the flame cannot come from the true focus. If they did, all the light from one panel would be emitted in absolutely parallel lines, and therefore in a revolving apparatus the beam would pass any given point on the horizon in an infinitely short period of time—to be precise, instantaneously. ”

“ The electric light was found to suffer to a much larger extent than either oil or gas light per unit of power by atmospheric absorption, but the infinitely greater total intensity of the beam obtainable by its use, both by reason of the high luminous intensity of the electric arc and its focal compactness, more than outweighed the higher percentage of loss in fog. ”

“ 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. ”

“ This tends to have a cascade effect on the atoms which have picked up the energy from outside, so that more and more of the light generated inside the tube tends to be parallel to the length of the tube. One of the mirrors is only partially silvered, and eventually the light bouncing back and forth becomes powerful enough to flash through the half-silvered end, giving a coherent beam of light. ”

“ If there is a parallel beam proceeding from a lamp, or from the sun, and it falls on the form of lens, called a convex lens, which bulges out in the middle, we learn from Fig. 27, that the upper part acts like the upper prism just considered and turns the light down, and the lower acts in the reverse manner and turns the light up, and the sides act in a similar manner ”

“ Transmission of rays through tourmaline is only one of several ways in which light can be polarised. When a beam of light is reflected from a polished surface of glass, wood, ivory, leather, or any other non-metallic substance, at an angle of 50° to 60° with the normal, it is more or less polarised, and in like manner a reflector composed of any of these substances may be employed as an analyser. ”

“ The laboratory being well filled with the fumes of incense, and sufficient time being allowed for their uniform diffusion, the electric beam was sent through the smoke. From the track of the beam polarised light was discharged; but the direction of maximum polarisation, instead of being perpendicular, now enclosed an angle of only 12° or 13° with the axis of the beam. ”

“ An experiment with a beam of light answers the question; for while it proves our ordinary air to be charged with floating matter, the beam pronounces air, which has been carefully filtered through cotton-wool, to be visibly pure; there are no germs afloat in it; hence it is impossible as a generator of life. ”