Speed of sound

“ The quality and intensity of sound do not alter the rate of speed. If this were not true, ensemble music would be impossible. Intensity of sound is greater in condensed air; velocity of sound is greater in a warm temperature. ”

“ The speed of propagation, which, as we have seen when discussing the measurement of the velocity of sound, depends very little on the musical note, is not at all the same in the case of the various radiations which can be propagated in the same substance. The index of refraction varies with the duration of the period, or, if you will, with the length of wave in vacuo which is proportioned to this duration, since in vacuo the speed of propagation is entirely the same for all vibrations. ”

“ This has been explained by the fact that owing to the resistance of the air to a body moving at first with a high velocity its speed is so reduced that it strikes the earth with a velocity less than that of sound. Hence the sound reaches the earth before the body strikes the ground. ”

“ Some thinkers suppose that the motion of bodies of that size must produce a noise, since on our earth the motion of bodies far inferior in size and in speed of movement has that effect. Also, when the sun and the moon, they say, and all the stars, so great in number and in size, are moving with so rapid a motion, how should they not produce a sound immensely great? ”

“ But light waves are always at right angle, different from sound waves, and we must come to the conclusion that light does not travel in a straight line, but in a series of curves. While its theoretical speed is 186,000 miles per second, its actual speed is many times that. ”

“ The knowledge we gain by experiment brings home to us what a miserably imperfect piece of mechanism our bodies are. The ear can detect the slow-footed sound vibrations that come to us at the rate of between 40 and 40,000 a second. But the whole of space may be quivering and palpitating with waves at all sorts of varying speeds, and our senses will tell us nothing of them until we get them coming to us at the inconceivable speed of 400,000,000,000,000 a second, when again we respond to them and appreciate them in the form of light. ”

“ The Nature of Sound.—We have observed that sound originates at a vibrating body, that it requires a medium in order to be transmitted from one place to another, and that it travels at a definite speed in a given substance. ”

“ While sound travels as vibrations of some material medium, light travels only as vibrations of the ether; solids, liquids, and gases act so as to hinder rather than to assist in its movement. That is, light travels best in a vacuum or in a space devoid of ordinary matter. (b) The speed of light is so great that at ordinary distances on the earth its motion is practically instantaneous. Experiments have shown that its speed is about 186,000 miles to 300,000 kilometers a second. ”

“ If, in fact, the amplitude of the vibrations acquired a noticeable value in comparison with the wave-length, the speed of propagation should increase with the amplitude. Yet, in spite of some curious experiments which seem to establish that the speed of light does alter a little with its intensity, we have reason to believe that, as regards light, the amplitude of the oscillations in relation to the wave-length is incomparably less than in the case of sound. ”

“ Chladni’s Tonometer: the Iron Fiddle, Musical Box, and the Kaleidophone
And now let us shorten our rod, so as to bring its vibrations into proper relation to our ears. When it is about four inches long, it emits a low musical sound. When further shortened, the tone is higher; and, by continuing to shorten the rod, the speed of vibration is augmented, until finally the sound becomes painfully acute. These musical vibrations differ only in rapidity from the grosser oscillations which a moment ago appealed to the eye. ”

“ I think there will be facilities for hearing, not only at a greater distance, but also through a more perfect medium, transferring sound with immensely greater velocity than it now travels through our atmosphere. We all know that sound is transferred, at sea level, where the air is dense, about eleven hundred and eighty feet in a second, taking almost five seconds to travel a mile, which is very slow motion, yet, very swift compared with the motion of our railway cars. Experiment has de-monstrated that with a more perfect medium for conveying it, sound will travel very rapidly. ”

“ What is it that these rays of light striking our retina convey to our brain, and from our brain to whatever is ourselves, in the seat of consciousness above this? What is this mysterious correspondence set up between something within and something without, that at times sends such a clamour of harmony through our whole being? Why do certain combinations of sound in music and of form and colour in art affect us so profoundly? What are the laws governing harmony in the universe, and whence do they come? It is hardly trees and sky, earth, or flesh and blood, as such, that interest the artist ”

“ We now come to one of the most delicate points in the whole theory of sound. The velocity through air has been determined by direct experiment; but knowing the elasticity and density of the air, it is possible, without any experiment at all, to calculate the velocity with which a sound-wave is transmitted through it. Sir Isaac Newton made this calculation, and found the velocity at the freezing temperature to be 916 feet a second. ”

“ If less time is taken in traversing the shorter road, propagation is not instantaneous, and the question is answered. But our physicist
will then show us that the points of silence succeed one another at equal intervals, and will deduce from this the length of the wave; and, if he knows the duration of the vibrations of the diapason, he will obtain, by these data, the velocity of the sound. ”

“ If we could augment the elasticity of air, without at the same time augmenting its density, we should augment the velocity of sound. Or, if allowing the elasticity to remain constant we could diminish the density, we should augment the velocity. ”

“ It would be a noise if the pavement should be irregular, but if the pavement is regular and the vibrations or beats are uniform, it is then called a sound. But you wanted to know why you saw the shot before you heard it. Simply because sound does not travel as fast as light. Sound moves 1,040 feet in a second, and light over 186,000 miles a second, which is about 850,000 times faster than sound. ”

“ The quickest vibrations which strike the eye, as light, have only about twice the rapidity of the slowest; whereas the quickest vibrations which strike the ear, as a musical sound, have more than two thousand times the rapidity of the slowest. ”

“ Again, you take metal rods and connect them together, and let a sound be made at the end remote from you, and it is found that, in some metals, the sound will travel many times faster along the metal rods than it will through the atmosphere; hence you see that the velocity of sound is really dependent upon the nature of the elements or substance through which it is conveyed. ”

“ It will be necessary now to prove experimentally that the same things can be done with sound, in order that a body of proof may be built up in your minds convincing you that the external cause of sound-sensation must be a wave-motion in the air. ”

“ Sound travels faster through solids than through liquids, and faster through liquids than through gases. In liquids, the relation of the elasticity to density is greater than in air, and in solids the relation is greater still. Therefore sound travels much faster in liquids than in gases, and faster in solids than in liquids.
This is the reason why a train can be heard coming if the ear is put to the railway-line, when no indication of its approach is given to the ear by the atmosphere. Some examples of the velocities of sound through different substances are as follows--
Art. ”

“ If I strike my pencil upon the table, I hear a snap that appears to the ear to be simultaneous with the stroke: if, however, I see a man upon a somewhat distant hill strike a tree with an axe, the sound does not reach me until some appreciable time has passed; and it is noted, that, the farther away the place where a so-called sound originates, the longer time does it take to reach any listener. Hence sound has in air a certain velocity which has been very accurately measured, and found to be 1,093 feet per second when the temperature of the air is at the freezing point of water. ”

“ Many experiments have been made to determine the velocity of sound, the most reliable of which vary not over seven feet per second. The average of six of the best experiments, made in the early part of the nineteenth century, is 1089.7 feet per second at 32° Fahrenheit. ”

“ If the fork made eleven hundred vibrations per second, each of these waves would be one foot long; for sound-waves of all lengths travel in air with the same rapidity. Some late experiments seem to show that the actual amplitude of motion of the air, when moved by such a high sound as that from a small whistle, is less than the millionth of an inch. ”

“ Although each atom of air moves a very little way forwards and then back, yet, as a long row of atoms may be crowded together before they begin to part, a wave is often very long. When a man talks in an ordinary bass voice, he makes sound-waves from 8 to 12 feet long; a woman's voice makes shorter waves, from 2 to 4 feet long, and consequently the tone is higher, as we shall presently explain. ”

“ If a light cork ball on the end of a thread is brought in contact with a sounding fork, the ball does not remain at rest, but vibrates back and forth, being driven by the moving prongs.
FIG. 165.—The ball does not remain at rest
These simple facts lead us to conclude that all sound is due to the motion of matter, and that a sounding body of any kind is in rapid motion.
251. Sound is carried by Matter. In most cases sound reaches the ear through the air; but air is not the only medium through which sound is carried. ”

“ As to the theory itself, it suggests a curious reflection, that nature might have caused sound to travel, not at the rate of 340 metres a second, and that its velocity, which depends on the density and the elasticity of the air, might have been very much less. ”

“ When a wave of sound travelling through one medium meets a second medium of a different kind, the vibrations of its own particles are communicated to the particles of the new medium, so that a wave is excited in the latter, and is propagated through it with a velocity dependent on the density and elasticity of the second medium, and therefore differing in general from the previous velocity. ”

“ The velocity of sound does not very much vary, whether it goes with the wind or against it. As sound moves vastly swifter than the wind, the acceleration it can thereby receive can be but inconsiderable ”