Signal light

“ Besides the various rockets, signal-lights have been constructed to be fired from guns and pistols. During the recent war the airman in the dark heights used the pistol signal-light effectively for communication. These devices emitted stars either singly or in succession, and the color of these stars as well as their number and sequence gave significance to the signal. Some of these light-signals were provided with parachutes and were long-burning ”

“ Light: The light of a field glass is expressed by a number which is the ratio of the amount of light which reaches the eye through the glass to the amount which enters the eye unaided. This comparison will be reached by means of the absorption apparatus [130] furnished by the Signal Corps. This apparatus consists of two wedge-shaped vessels made of brass with glass windows in the sides, and are filled with a perfectly black liquid. The sky line is first viewed through the apparatus with the naked eye and the instrument adjusted to limit of visibility. ”

“ When a number of stations are in view from one station and it is desired to send a message to all or more than one station, some preconcerted signal, as a rocket, a red light, or some peculiar flag or torch signal, should be designated as a signal for general attention. ”

“ Three or four lights in a row about five feet in length would thus suffice for giving an engineer his signal a mile before he passed the post. A space signal given in some such way would naturally require more feeding of electricity or gas or oil—than does the single small wick flame that now gives forth the colored beam. But on the whole it would perhaps be well to spend fuel and light rather than life. ”

“ Movement imparted by these screws to the mirror does not disturb the alignment, as its center (the unsilvered spot) is at the intersection of the axes of revolution. Extra care bestowed upon preliminary adjustment is repaid by increased brilliancy of flash. With the alignment absolutely assured and the "shadow spot" at the center of the disk, the axis of the cone of reflected rays is coincident with the line of sight and the distant station receives the greatest intensity of light. Remember the distant observer is unquestionably the better judge as to the character of the flash received ”

“ The Ardois system is a special system of night signaling designed to utilize combinations of red and white signal lights in forming the elements of any desired alphabet. Four signal lamps capable of displaying either red or white lights are attached at convenient intervals to a vertical cable or staff rigged between the top of a mast and the deck, if on shipboard, or the ground, if on shore. Illumination is furnished by electrical means and any desired combination of lights is automatically obtainable by operating a keyboard. ”

“ Telescopes, the object glasses being equal in size, diminish light as a general rule in proportion as their magnifying power is great. The most powerful glasses are therefore to be used for minute observations on the clearest days or when there is a strong light upon the observed object. ”

“ Any luminous source such as the sun, a candle flame, or an incandescent lamp is sending forth electromagnetic waves not unlike those used in wireless telegraphy excepting that they are of much shorter wave-length. The eye is capable of recording some of these waves as light just as a receiving station is tuned to record a range of wave-lengths of electromagnetic energy. ”

“ Short waves, long waves, micro-waves, frequency-modulated waves, amplitude-modulated signals, every conceivable type of radiation signal, was beamed at the small, invisible, hurtling objects as they swung madly about the globe. ”

“ 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! ”

“ 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. ”

“ When the sun failed to shine, or was not convenient, I practiced looking at a large incandescent electric light, and very soon the artificial lights troubled me no more than the stars which twinkle in the heavens at night ”

“ If our eyes were sensitive to these frequencies, both of which are composed, as is also light, of electro-magnetic rills, we could see anything that was happening anywhere in the world, for they go through matter as though it did not exist, as light passes through glass; indeed, if our region of Sight waves was only put an octave lower we could not use glass in our windows, it would be too opaque, we should be obliged to have our windows made of thin slabs of carbon or other substances permeable to Radiant heat waves. ”

“ In some cases the telescope is dispensed with, a vertical wire is illuminated by a lamp placed behind it, and the mirror is a concave one, which forms the image of the wire on the scale as a dark line across a patch of light. ”

“ The Chief Signal Officer of the Army reserves the right to inspect any or all processes of manufacture, and unsatisfactory material will be marked for rejection by the inspector before, during, or after assembly, as occasion may arise.
Each glass will be tested for power, field, definition, and light. Any glass which is not the equal of the sample and model in all respects will be rejected. ”

“ 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. ”

“ 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. ”

“ Light is an electromagnetic disturbance of the ether. Optics is a branch of electricity. Outstanding problems in optics are being rapidly solved, now that we have the means of definitely exciting light with a full perception of what we are doing, and of the precise mode of its vibration. ”

“ 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.” ”

“ A high-power glass is unsuitable for use at night, hazy atmosphere, or for use of a mounted man where the glass can not be rested against a firm support. A low-power glass with large object lens to permit as much light as possible is a necessary condition for use at night. ”

“ Pushing the movable screen toward the visible spectrum, at a distance of three or four feet beyond the violet, where only darkness existed before, light begins to appear. On pushing in the screen, the whole ultra-violet spectrum falls upon it, and is rendered visible from beginning to end. The spectrum is not continuous, but composed for the most part of luminous bands derived from the white-hot crucible in which the metals are to be converted into vapor. ”

“ Just before total reflection, a series of images of the slit are seen reflected by the air-film. When white light is used, and the image is observed through a direct vision spectroscope, interference bands are observed in the spectrum, which flit across it with the slightest rotation of the cylinder. ”

“ The colour and the position in the spectrum both depend on the interval between one wave and the next, so that if a body giving out light of a particular wave-length, e.g. the blue light corresponding to the F line of hydrogen, is approaching the observer rapidly, the line in the spectrum appears slightly on one side of its usual position, being displaced towards the violet end of the spectrum; whereas if the body is receding the line is, in the same way, displaced in the opposite direction. ”

“ Our recent telescopes have, therefore, concave plate-glass mirrors, twenty metres in diameter, like those used for converging the sun's rays in solar engines, but with curves more mathematically exact, which collect an immense amount of light and focus it on a sensitive plate or on the eye of the observer, whose back is turned to the object he is studying. An electrical field also plays an important part, the electricity being as great an aid to light as in the telephone it is to sound. ”

“ 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. ”

“ 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. ”

“ When brought in contact, the oxygen in the water decomposes the calcium in the carbide, and in this decomposition the hydrogen in the water is liberated and unites with the carbon of the carbide, forming a hydrocarbon gas which is acetylene. It is a pure white light of intense brilliancy and high candlepower. The spectrum analysis of acetylene shows that it is almost identical with sunlight, and in consequence delicate shades of color appear according to their true value as under the light of the sun, consequently it penetrates fog to a greater distance than other lights. ”

“ When no fog is present the gas-lights in the distance and close to are of the same colour and brightness, showing that their change in appearance is simply due to the misty atmosphere intervening between them and the observer. We can imitate the light from the sun, after its passage through various thicknesses of atmosphere, in a very perfect manner in the lecture-room, using the electric light as a source. A condensing lens is put in front of the lamp, and in front of that a circular aperture in a plate. ”

“ A better example of wireless is a lighted lamp and your eye, for in this case the lighted lamp acts as a transmitter and sets up very short waves in the ether, which are called light waves and these likewise travel in every direction. The ether is a substance that is 15 trillion times lighter than the air and it fills the whole universe, and when the electric waves set up by a light in it strike your eye the optic nerve carries the sensation of them to your brain and you see the light. ”

“ When the letters of the alphabet are to be used to indicate the meaning set opposite them in the following tabulation, the upper light of the display is pulsated. This is effected by means of a special pulsating key. Special signification is not given "I" and "T," they being represented by a single lamp.
Before numerals are made, the distinctive signal for "numerals" "X" is shown and the upper light is pulsated, which serves still further to distinguish them from letters. ”

“ When light falls on a transparent body, part is reflected and part is refracted. The angle which the ray makes with the normal, or perpendicular, to the surface at the point of contact is known as the angle of incidence, and the angles which the reflected and refracted rays make with the same normal are known respectively as the angle of reflection and refraction. ”

“ The rays of light emerging from the ocular of the Galilean telescope are divergent and cover an area much greater than the size of the pupil of the eye. As all rays falling outside the pupil of the eye are lost, but a small field of view can be seen, as in looking through [108] an ordinary cone from the larger end. The prism glasses are constructed on the opposite principle. The rays of light gathered by the objective emerge from the eyepiece in a converging pencil of light small enough to enter the pupil of the eye, thus giving a larger field of view ”

“ Electrical theory.—The second, or electrical, theory supposes that the visual impulse is the concomitant of an electrical impulse; that an electrical current is generated in the retina under the incidence of light, and that this is transmitted to the brain by the optic nerve. There is much to be said in favour of this view, for it is an undoubted fact, that light gives rise to retinal currents, and that, conversely, an electrical current suitably applied causes the sensation of light. ”