produce the greatest variety of tones with unisons of vibration, or an exact recurrence of vibrations after the nearest intervals. 614. The strings of a piano-forte, harp, or violin, are brought into accordance or successive octaves, or recurring tones, by the accuracy of the ear. In the harp, &c., their lengths are exactly proportioned to the scale by the maker, but as the strings vary in their tension, owing to the weather and other causes; and as they cannot all have the same precise bulk, it is necessary, from time to time, to tone them; which means nothing more, than making each perform its proper number of vibrations in relation to the other strings. 615. These seven notes, then, are the basis of all music; and, with the addition of five half tones, are the alphabet of music, and fill all the concordant intervals of one octave. Octaves may, however, rise upon each other in successive ratios or degrees, as in the piano-forte, which has 5 and even 7 octaves; or 5 sets of natural notes as above, and 5 semi-tones, or flats and sharps to each octave. 616. For the purpose of obtaining further variety in composing tunes or melodies, these several tones may be played shorter or longer; and, in this respect, are divided as under : 2 minums make 1 semi-breve ; 2 demi-semi-quavers make 1 semi-quaver; 32 demi-semi-quavers are to be played in the time of one semi-breve. Again in regard to the tune itself, there are also two sorts of time, slow and quick, as common time and treble time. 617. When an agreeable succession of simple notes, having a perfect beginning and ending, is played or sung, it is called a tune, an air, or melody; as a song, hymn, dance, or march, according to its several purposes. When these notes, forming an air, are combined with corresponding notes, in different octaves, or on other instruments, and the whole is scientifically made to produce a concordant and agreeable effect, it is called Harmony. The bass and treble of a piano-forte played at the same time with the left and right hand, constitute the most common practice of harmony. Some of Handel's pieces have been played by 1000 instruments and voices, all sounding harmoniously together. : Obs. The human soul may be moved in all its passions by music and as a soother of the mind, and a source of exquisite pleasure, the practice on some instrument cannot be too strongly recommended as a branch of liberal education to children of both sexes. XXVIII. Of Physics; or, the General Properties of Matter. 618. All existence is, what it appears to be to the powers of our senses; and is, therefore, relative, or comparative, to those powers. Thus, there is no intrinsic sweetness in sugar; but the quality of sweetness is in the sense of the palate. In a violet, there is no inherent colour; but the sense of colour, called violet, is in our optic nerve; and the sense of sweetness produced by the same flower, is in the olfactory nerve. So, there is no sound in a vibrating string; but the sound, so called, is the vibrating effect produced on our auditory nerves. And the sense of hardness, or substance in a stone, arises from its being harder than our fingers, which have not power to pass through it. Obs. It has been a favorite notion of ancient and modern philosophers, that the substratum or basis of all matter is the same; and that all the varieties exhibited to our senses, are only so many modifications, capable of producing their respective sensible effects. 619. A person, born blind, has no sense or conception of colours: he can feel the hardness, the roughness, and the length and breadth of surfaces; but he can have no perception of their various colours. So, one born deaf, sees the motion of a bow on a violin, or the sticks on a drum: but has no idea of their sound. In like manner, all food is alike, in flavour, to those who have lost their sense of taste and smell. 620. The sensations produced by things out of ourselves, are called our perceptions; and the property or power of bodies to excite or create particular perceptions, is, in common language, considered as the perception itself; and the body is considered as possessing the sensation itself, which it only creates in us. Thus, we call vinegar sour, oil smooth, and fire hot; though the sense of sourness, smoothness, and heat, is in us, not in the bodies which create those perceptions. So, likewise, in common language, we talk of the motion of the sun and stars; though it is only our earth that moves. 621 Every collection, then, of properties, capable of affecting our senses, is called material, or matter; and it possesses extension or bulk ; solidity, or the power of maintaining its space; divisibility, or the capability of being divided into infinitely small parts and a power, or disposition to coalesce or unite with other matters. Without external force, such matter is inert or dead; but it may be put in motion by powers sufficient to overcome its inertness, or its disposition to unite with larger masses. So, also, motion, once acquired, would continue for ever, if not checked by opposing powers, or by friction. The disposition of all matter to rush or fall together, is usually called attraction; and is supposed by Sir Isaac Newton and others, to arise from effluvta emitted from the respective bodies. Obs. This idea has been combatted by Sir Richard Phillips, in the Monthly Mag. Oct. 1, 1811. He asks, how any effluvia can take hold of distant bodies; and what connection can exist between such effluvia, and the body whence they flowed, to occasion them to solicit another body, to return with them back to it? He then suggests, that all space is filled with an ethereal, elastic medium, except in the points occupied by matter, as the Sun, Stars, and planets; that this medium solicits to enter the foreign substances of matter, in degrees proportioned to their density and peculiar construction; that these forces act in right lines infinitely extended from the substance; that the phenomenon of attraction arises from the interception of those infinite lines by other bodies; that the forces must then be FINITE in the direction of any two substances, but INFINITE in other directions. ; and that, of course, all bodies must fall towards each other in the line which joins their centres; because they are pressed FINITELY in that direction, but INFINITELY in every other. Thus, bodies are pressed to the earth, by forces infinitely extended in their zenith; but the action of those forces in their nadir is taken off, by the interpo. sition of the mass of the earth. So, likewise, the pressure on the earth is always diminished on the side immediately next the sun; while it is infinite on every other side; and that pressure necessarily produces the phenomena called attraction. 622. Extension is infinite; at least the human mind can set no bounds to it, but can add millions to millions of miles in every direction. Such matter as affects our senses, is, however, not visible every where; but the spaces between the stars and planets are supposed to be filled with a rare, elastic medium. Solidity is a relative idea; and is measured by us, in the ratio of the attraction to the earth called weight. A cubic foot of platina weighs as much as 92 cubic feet of cork, or as 230,000 cubic feet of hydrogen gas; yet the platina itself may be light compared with other bodies unknown, and the cork and the gas be heavy in regard to others. Obs.-The whole earth, in solid matter, might, per haps, be compressed in the compass of an orange; just as 1000 cubic feet of elastic steam can be re-compressed |