bserved also that the more sonorous bodies, when truck under water, gave a less vivid impression nan others less sonorous. These experiments were successfully repeated by the late Dr. Monro, f Edinburgh. SONOROUS SUBSTANCES. All bodies are not equally fitted for producing sound. Those which have the greatest degree of lasticity appear to be the most sonorous. It is wing, indeed, to the great expansible force and elasticity of the air, that gunpowder and the elecric flash, by rending it and forming a vacuum, occasion the loud sounds which often strike us with error. The cracking of a waggoner's whip affords a good illustration of the sound of thunder or any other explosion. The sudden jerk of the end of the whip-cord displaces a portion of air, and forms an empty space into which the adjacent air violently rushes. The air which formed the several sides of this empty space, thus collapsing with a shock, produces the sound. The changes which take place among the minute particles of bodies, in consequence of the vibrations from which sounds arise, are remarkably different in metals, in wood, and in musical strings. This can be illustrated in the case of metals, by repeating the experiments of Dr. Chladni of Berlin, who took plates of different metals, and having strewed them with fine sand, caused them to sound by drawing over their edge the bo▾ of a violin. In these experiments the sand is found to arrange itself according to the vibrations produced; and it is curious that the form which the sand takes is different in different metals. A body can easily repeat those experiments wi sheet-lead, sheet-iron, copper-plates, &c. MUSICAL STRINGS. In the case of musical strings, as in other sound ing bodies, the quicker they vibrate the mot sharp is the sound; and this does not depend at a on the slowness or quickness with which you stri them, but on the tension and thickness of th string. We are told, but on the authority d what experimental calculation we know not, that the gravest sound which the ear can perceive is formed of two thousand vibrations in a second, and the sharpest sound, of twelve thousand. Thus in the piano-forte and the harp, the high treble notes are produced by short, small, tight strings, and the deep low bass notes by strings which are long, thick, and little stretched. NATURE OF HARMONY. On striking a bell or a musical string once, we may hear by minute attention, first, the fundamental sound or note; secondly, the octave or eighth note above; thirdly, the twelfth; and lastly, the seventeenth. These are called harmonic notes. It is from the vibrations of several strings taking place in a certain order that agreeable or disagreeable feelings are excited. The sounds producing these opposite feelings, are said to be harmonious or to be discordant. For example, if the vibrations of two strings are performed in equal times, the same tone is produced by both, and they are said to be in unison. Again, if one string vibrate in half the time of another, the first vibration of the latter will strike upon the ear at the very same instant as the second vibration of the former. These will accordingly agree or harmonize, and their concord is by musicians termed an octave or eighth, because there are eight distinct tones inclusive between the tones of the two strings. If the second vibration of the first string strike the ear at the same instant with the third vibration of the second string, the compound sound or concord is termed a fifth, for a similar reason. When the vibrations of two or more strings strike the ear at different instants, they are said to jar, or to produce discord. To make this explana tion of harmony and discord the more intelligible, the following simple experiment may be made. Suspend a ball of thread and poise it in the air, giving it a push with your finger. If you wish to carry on the swinging motion, you must wait till the ball is on the point of turning before you give it another push. If you touch it in the middle of a swing you will cause it to stop. This is exactl the case with the air which is swung by a harp string, or put in motion by a flute; for in this respect wind-instruments are the same with the harp. The first case illustrates harmony; the last, discord. On these principles, we imagine that a person who is deaf, if his eye were sufficiently quick, might perhaps be able to tune a harp or a piano-forte with tolerable exactness. We are not indeed aware of any instance of this, and merely hint its possibility. ANIMATED SOUNDS. Although none of the inferior animals can articulate, with the exception of parrots and a few other birds; yet almost every animal can emit some species of sound. Fish, indeed, so far as is known, are altogether mute. The organs of voice in the larger animals are more imperfect in their powers of intonation, though similar in construction to those of man; and savages easily imitate the sounds of animals. In the same species, climate seems to have an influence over the voice, if it be true, as we are assured, that European dogs lose their power of barking when taken to the West Indies, where the native dogs cannot bark. The sounds produced by insects are not the least observable among those which attract our attention in our walks. Nor undelightful is the ceaseless hum, To him who muses through the woods at noon; THOMSON. Insects, however, have not organs similar to those of the voice in other animals; that is, they never use their mouth for the purpose of making sounds. Accordingly, the buz of flies, the hum of bees, the chirp of crickets, the crink of grasshoppers, the drone of beetles, the whiz of dragon flies, the song of the cicâdæ, and the ominous click of the death-watch, are all produced by the wings, or other parts of the insect, either rapidly beating the air, or striking against the parts near them, or on wood, stones, and other sonorous substances. Some of the cicâdæ have a finely contrived drum, whose |
