is now to be poured on, being first reduced to a proper strength by vinegar or water. Let it stand five minutes for the first shade, then pour it off and wash and dry the plate. Then stopping up the light with the varnish, pour on the acid for the second tint, and let it stand five miputes more, and proceed in this manner for every tint till you have produced the darkest shades. In etching landscapes, the sky and distant objects are performed by a second operation, and the application of a fine powder. Sandby, Parkyns, and Jukes, have been eminent in this branch of engraving.

4. Mezzotinto. Prince Rupert, of Germany, first invented this particular manner of representing figures on. copper, so as to form prints in imitation of painting in Indian ink. The method is very different from common engraving. To perform it, the surface of the plate is traversed all over, with an instrument termed a grounding tool made on purpose, first one way, and then the other, across, &c. till the surface of the plate be entirely furrowed with lines close to each other, so that if an impression was then taken from it, it would be one uniform mass of black. This done the design is drawn, or marked, on the same face; after which they proceed with burnishers, scrapers, &c. to expunge or take off the rough ground made by the tool, until they come to the surface of the copper, in all the parts, where the lights of the piece are to be, and that more or less, as the lights are to be stronger or fainter; leaving those parts black which are to represent the shadows or deepenings of the draught. The instruments used in this kind of engraving are cradles, scrapers, and burnishers. The art of scraping mezzotintos has been applied to the printing with a variety of colours, in order to produce the resemblance of paintings.

5. Stippling is performed by making dots on the copper, and working the plate in such a manner as to have somewhat the appearance of a mezzotinto; but infinitely preferable, as it affords a softer, and yet more spirited effect. It is also a species of engraving in imitation of chalk drawings. Ryland and Bartolozzi were the most distinguished in this art.

6. Calcography. This mode of engraving is a modern invention by Hassell, to imitate pencil, chalk, and pen and ink drawings, for which he has been rewarded and honoured

by the Society of Arts, with their medal and a purse of thirty guineas. For particulars of this art, see Hassell's Calcographia.

7. Coloured Engravings. (1.) About the time of the revival of learning, some artists produced prints of differents colours, by means of wood-cuts, employing a dif ferent plate for each colour. But so much inconvenience and imperfection attended this method, that it was seldom resorted to. No further improvement was attempted, till near the middle of the eighteenth century, when somexperiments were made by French artists, with copperplates, with a view to obtain coloured prints. They also ⚫ found it necessary to use different plates for different parts of the work; and on this, as well as other accounts, the expense of their plan prevented its general adoption. Towards the close of the last century, a method was invented in England of producing an elegant coloured engraving from a single copper-plate.

(2.) Mr. J. R. Smith, an engraver, of London, invented a method of taking impressions from his own plates, which so nearly resembled oil-paintings, as to be, with difficulty, distinguished from them by connoisseurs. These impressions are said to possess that sort of brightness, which is so much admired in Venetian paintings-to resemble them also in permanency--and, to be of such a nature as to render a covering of glass, so expensive and frangible a material, altogether unnecessary. A method of engraving closely resembling drawings, was invented by that cele brated artist Mr. Westall. In 1799, he exhibited a drawing, and the year following a print taken from it, which was so close an imitation, as completely to deceive the eye.

III. ENGRAVING ON STEEL, or DYE SINKING. This is chiefly used in cutting seals, punches, matrices, and dies for striking coins or medals. The method of engraving with the instruments, &c. is the same for coins as for medals and counters; the only difference is in the relievo, that of coins being less than that of medals, and that of counters less than that of coins.. Engravers in steel commonly begin with punches, which are in relievo, and serve for making the creux, or cavity, of the matrices and dies: though sometimes they begin with the creux, but only avhen the work is to be cut very shallow.

IV. ENGRAVING ON PRECIOUS STONES. In engraving diamonds, the first thing is to cement two rough diamonds to the ends of two sticks, held steadily in the hand, and rub or grind them against each other, till they are brought into form. The powder serves to polish them, which is performed with a mill turning an iron wheel, The diamond is fixed in a brass dish, and applied to the wheel, and covered with diamond dust, mixed with oliveoil, and first one face, then another is applied to the wheel. Rubies, sapphires, and topazes, are cut and formed on a copper wheel, and polished with tripoli diluted in water. Agates, amethysts, emeralds, rubies, and the softer stones, are cut on a leaden wheel, moistened with emery and water, and polished with tripoli, on a pewter wheel. Lapis-lazuli, opal, &c. are polished on a wooden wheel. To fashion and engrave vases of agate, crystal, &c. a lathe is used on which are the tools, turned by a wheel; and the vessel is held to them to be engraven, either in relievo or otherwise; the tools being moistened, from time to time, with diamond-dust and oil, or emery and water.

V. ENGRAVING ON GLASS. To effect this kind of engraving, a glass-plate is covered with melted wax, or mastic. When this coating becomes hard, it is engraven upon by a very sharp-pointed needle, or other instrument of that kind. A mixture of oil of vitriol and fluoric acid, is then put upon the plate, and the whole covered with an inverted china vessel, to prevent the evaporation of the acid. In two days the plate being cleared of its coating, exhibits all the traces of the instrument. It succeeds very well in the outline representation of philosophical instruments and chemical apparatus. The fluoric acid was discovered by Margraaf and Scheele.

Select Books on Engraving.

Landseer's Lectures on Engraving, delivered at the Royal Institution, svo. Meadows' Lectures on Engraving, delivered at the Surry Institution, 8vo. Gilpin's Essay on Prints, 12mo. Hassell's Calcographia.

CHAP. VII.-MUSIC.

1. MUSIC is both an art and a science, and in either case, its object is the combining of sounds in a manner that shall be agreeable to the ear. This combination may be

either simultaneous or successive: in the first case, it constitutes harmony; in the last, melody.

The science of music is twofold; for it may respect the investigation and development of the causes of sounds, and the philosophical nature and distinction of concords and discords; or it may be directed to the prescription of rules for composition, or for combining sounds either in melody or in harmony, or in both, so as to be agreeable to the ear. So again the art of music is twofold; for, it may relate to the invention and structure of different kinds of instruments, or it may refer to the practice of singing, and of performing upon the different kinds of musical instruments. The latter is, in a restricted sense, called the art of music.

The gravity or acuteness of a sound depends entirely upon the number of vibrations of the sonorous substance, whatever it may be, in a given time.* The more rapid the vibrations the acuter the tone, and vice versa. When the vibrations occur in exactly equal times, the sounds yielded are called unisons. If the times of vibration be as one to two, the sounds generated are, at the interval, called an octave. When a male and female voice sing the same air, they proceed throughout at the interval of an octave. Between the two extremes of an octave, other notes are interposed, and to these names are given. Foreigners have usually employed the names Ut, Re, Mi, Fa, Sol, La; but the first seven letters of the alphabet are more generally employed. If one extreme of an octave be denoted by the letter C, for example, then will the other extremity be C also, and the intermediate notes, proceeding from grave to acute, will be D, E, F, G, A, B. These, however,. do not constitute equal intervals, the space between E and F, and that between B and C, being only semitones, while all the other intervals are tones. The octave, then, contains twelve semitones; and the places of these are changed by means of fluts and sharps, and in a manner on which depends the place of the key or fundaınental

note.

2. The vibrations of a musical string are easily determined mathematically, by means of the following formula. Let W represent the weight of a musical string, L its

* See the article, ACOUSTICS.

length, P the tending or stretching force, g the space described by a falling body in one second of time, then will T, the time of vibration of the string, be ́=

LW

2 g P

From this the absolute frequency of sound may be ascertained; and the real place of the note, from the relation of its number of vibrations in a second to 250 or 256, the latter of which may be assumed as a very convenient standard for the vibrations in a second when the note yielded is the C denoted by the mark of the tenor cliff.

3. In a simple composition, all the intervals are referred to a single fundamental or key note. All audible sounds are considered as repetitions of a series within the interval of an octave. One third of a chord in length, and equally stretched, would yield, on being made to vibrate, the fifth above the superior octave, one fourth of the chord the double octave, and one-fifth the third above it. Thus, we have the common chord, or harmonic triad, that is, the fundamental note with its third and fifth, constituting the most perfect harmony; being also the foundation of the most simple and natural melodies. The intermediate steps are supplied by completing the triad of the fifth, which gives us the seventh, in the ratio of 8 to 15, and the seIcond in the ratio of 8 to 9; and the triad in which the key note is the fifth, whence there result the fourth and sixth, in the ratio of 3 to 4 and 3 to 5. From this it follows, that if a musical string and its parts, or eight separate strings, be equally stretched, and in proportion to one another as the numbers 1, &,,,,,,, their vibrations will exhibit the natural, or diatonic series of sounds in the octave.

4. In a long piece of music the ear becomes fatigued unless the fundamental note is changed: one of the auxiliary triads, therefore, is taken for the fundamental harmony; and sometimes the modulation is continued till every note of the scale becomes a key note; the transpositions being effected by means of flats and sharps. For still farther variety we change the place of the middle note of the three triads, placing the minor third, or the interval of 5 to 6, below the major, or 4 to 5; and the scale thus formed is called the minor mode in contradistinction to