PLATE I. FIG. 4, 5, 6, 7. Specimens of an unknown Fossil Ve- getable.. PLATE III. page 237 FIG. 3. Chaotic State of the Earth ... 4. Intermediate State at the Formation. 259 260 5. The Earth in its present habitable State.... 263 PLATE IV. FIG. 1. Proportional Vibration of Musical Strings.. 3. Effect of equal Degrees on a Musical String 5. The Seven Diatonic Degrees. 6. Refraction of Air producing Musical Sound.. ment.... 8. Scheme of Reverted Harmonics 8. Harmonic Proportion of a Cross... PLATE V. FIG. 1. Petrified Fruit of the Arum.... 2 and 3. Echinites Pentaphylloides, or Rofaceous Echinite.. 19 $2 35 36 77 67 65 93 81 .... 134 175 a, b, c, &c. Fossil Fruits from Sheepy Island, 234, 132 PLATE VI. Specimen of a Petrified Scaly Fish in Stone ... 181 PLATE VII. Nineteen Figures of the Classes of Fossils, par- ticularly explained..... PLATE VIII. 229, &c. FIG. 1. A Valley in the Peak of Derbyshire..... of a Mile.... PLATE IX. 278 ibid. FIG. 1. A Section of the Strata, to shew their Trapping, 291 232 nified.. DISCOURSE VI. On the Philosophy of Musical Sounds. 1. OF SOUND IN GENERAL. WO things are generally necessary to TWO the production of sound; a sonorous body, to give the impression; and a medium, as a vehicle to bring it to the ear. Sonorous Bodies. The sonorous bodies of most effect are those endued with an elastic property, whose parts are so formed and accommodated to cach other as to be capable of a vibratory motion when they are forcibly struck by any kind of plectrum. Silver, copper, and iron, which are elastic metals, are also sonorous; but lead, which is unelastic, gives no sound. Tin, which by itself has but little more sound than lead, improves the tone of copper very much when VOL. X. B when added to it: ten parts of copper, with one part of tin, form that composition which is called bell-metal; and it is very extraordinary, that two metals, each of which has ductility when separate, (though tin has but little,) should unite into a third substance almost as brittle as glass. So wonderful is the power of tin in this respect, that even the vapour of it, when it is in fusion, will give brittleness to gold and silver, which are the most ductile of all metals. This effect of tin in improving the tone of copper may appear less mysterious, when it is known that a certain quantity of tin may be added to a mass of copper without increas-, ing the bulk of it; as I was informed by an ingenious artist, who had very large concerns. in this way. Brass, copper, silver, and iron, for their elasticity, are formed into musical strings for instruments. The common fiddle-string is made of the gut of an animal, clarified, twisted, and dried, and is remarkably elastic; as are likewise the hairs of the bow which are applied to it. No kind of wood being more elastic than fir, from its fibrous construction, it is the most proper for musical instruments, and was therefore applied to that use by the Hebrews Hebrews from the most remote antiquity. See 2 Sam. vi. 5. The classes of sonorous bodies are chiefly these three: 1. Bells of various figures and magnitudes, none of which have so pure and elegant a tone as those which are made of glass, which gives a powerful sound from its very great elasticity. 2. Pipes of wood or metal, which are nearly allied to the human voice, and may be made to imitate it very nearly, by means of a vibrating plate of metal, which performs the office of the larynx. 3. Strings either of a metallic or animal substance; which give sounds more grave or more acute according to their thickness, length, and tension. When fir-wood is combined with strings, or strings agitated by horse-hair, one sonorous body is assisted by another. It was observed above, that some sonorous body is generally necessary to the production of sound but in those concussions of the air which are occasioned by explosions from fired gunpowder, the air acts as a plectrum upon itself. The sudden expansion of that air which is confined propagates a vibratory motion to the air that lies next it, and so on, till the motion is spent. B 2 Sound |