enabled to imitate it, if you incline so to do, without being at the expense and trouble of the many experiments I have made in endeavoring to bring it to its present perfection. You have doubtless heard the sweet tone that is drawn from a drinkingglass, by passing a wet finger round its brim. One Mr. Puckeridge, a gentleman from Ireland, was the first who thought of playing tunes, formed of these tones. He collected a number of glasses of different sizes, fixed them near each other on a table, and tuned them by putting into them water, more or less, as each note required. The tones were brought out by passing his fingers round their brims. He was unfortunately burned here, with his instrument, in a fire which consumed the house he lived in. Mr. E. Delaval, a most ingenious member of our Royal Society, made one in imitation of it, with a better choice and form of glasses, which was the first I saw or heard. Being charmed with the sweetness of its tones, and the music he produced from it, I wished only to see the glasses disposed in a more convenient form, and brought together in a narrower compass, so as to admit of a greater number of tones, and all within reach of hand to a person sitting before the instrument, which I accomplished, after various intermediate trials, and less commodious forms, both of glasses and construction, in the following manner. The glasses are blown as near as possible in the form of hemispheres, having each an open neck or socket in the middle. The thickness of the glass near the brim about a tenth of an inch, or hardly quite so much, but thicker as it comes nearer the neck, which in the largest glasses is about an inch deep, and an inch and half wide within, these dimensions lessening as the glasses themselves diminish in size, except that the neck of the smallest ought not to be shorter than half an inch. The largest glass is nine inches diameter, and the smallest three inches. Between these three are twenty-three different sizes, differing from each other a quarter of an inch in diameter. To make a single instrument there should be at least six glasses blown of each size; and out of this number one may probably pick thirty-seven glasses (which are sufficient for three octaves with all the semitones) that will be each either the note one wants or a little sharper than that note, and all fitting so well into each other as to taper pretty regularly from the largest to the smallest. It is true there are not thirty-seven sizes; but it often happens that two of the same size differ a 1 See Plate 1.-A. note or half note in tone, by reason of a difference in thickness, and these may be placed one in the other without sensibly hurting the regularity of the taper form. The glasses being chosen, and every one marked with a diamond the note you intend it for, they are to be tuned by diminishing the thickness of those that are too sharp. This is done by grinding them round from the neck towards the brim, the breadth of one or two inches, as may be required; often trying the glass by a well-tuned harpsicord, comparing the tone drawn from the glass by your finger, with the note you want, as sounded by that string of the harpsichord. When you come nearer the matter, be careful to wipe the glass clean and dry before each trial, because the tone is something flatter when the glass is wet, than it will be when dry;—and grinding a very little between each trial, you will thereby tune to great exactness. The more care is necessary in this, because if you go below your required tone, there is no sharpening it again but by grinding somewhat off the brim, which will afterwards require polishing, and thus increase the trouble. The glasses being thus tuned, you are to be provided with a case for them, and a spindle on which they are to be fixed. My case is about three feet long, eleven inches every way wide within at the biggest end, and five inches at the smallest end; for it tapers all the way, to adapt it better to the conical figure of the set of glasses. This case opens in the middle of its height, and the upper part turns up by hinges fixed behind. The spindle, which is of hard iron, lies horizontally from end to end of the box within, exactly in the middle, and is made to turn on brass gudgeons at each end. It is round, an inch diameter at the thickest end, and tapering to a quarter of an inch at the smallest.-A square shank comes from its thickest end through the box, on which shank a wheel is fixed by a screw. This wheel serves as a fly to make the motion equable, when the spindle, with the glasses, is turned by the foot like a spinning-wheel. My wheel is of mahogany, eighteen inches diameter, and pretty thick, so as to conceal near its circumference about 25lb. of lead.-An ivory pin is fixed in the face of this wheel, and about four inches from the axis. Over the neck of this pin is put the loop of the string that comes up from the moveable step to give it motion. The case stands on a neat frame with four legs. To fix the glasses on the spindle, a cork is first to be fitted in each neck pretty tight, and projecting a little without the neck, that the neck of one may not touch the inside of another when put together, for that would make a - jarring. These corks are to be perforated with holes of different diameters, so as to suit that part of the spindle on which they are to be fixed. When a glass is put on, by holding it stiffly between both hands, while another turns the spindle, it may be gradually brought to its place. But care must be taken that the hole be not too small, lest, in forcing it up, the neck should split; nor too large, lest the glass not being firmly fixed should turn or move on the spindle, so as to touch and jar against its neighboring glass. The glasses thus are placed one in another, the largest on the biggest end of the spindle which is to the left hand; the neck of this glass is towards the wheel, and the next goes into it in the same position, only about an inch of its brim appearing beyond the rim of the first: thus proceeding, every glass when fixed shows about an inch of its brim (or three quarters of an inch, or half an inch, as they grow smaller) beyond the brim of the glass that contains it; and it is from these exposed parts of each glass that the tone is drawn, by laying a finger upon one of them as the spindle and glasses turn round. My largest glass is G, a little below the reach of a common voice, and my highest G, including three complete octaves.-To distinguish the glasses the more readily to the eye, I have painted the apparent parts of the glasses within side, every semitone white, and the other notes of the octave with the seven prismatic colors, viz. C, red; D, orange; E, yellow; F, green; G, blue; A, indigo; B, purple; and C, red again;-so that glasses of the same color (the white excepted) are always octaves to each other. This instrument is played upon, by sitting before the middle of the set of glasses as before the keys of a harpsichord, turning them with the foot, and wetting them now and then with a sponge and clean water. The fingers should be first a little soaked in water, and quite free from all greasiness; a little fine chalk upon them is sometimes useful, to make them catch the glass and bring out the tone more readily. Both hands are used, by which means different parts are played together.-Observe, that the tones are best drawn out when the glasses turn from the ends of the fingers, not when they turn to them. The advantages of this instrument are, that its tones are incomparably sweet beyond those of any other; that they may be swelled and softened at pleasure by stronger or weaker pressures of the finger, and continued to any length; and that the instrument, being once well tuned, never again wants tuning, In honor of your musical language, I have borrowed from it the name of this instrument, calling it the Armonica. With great esteem and respect, I am, &c. B. FRANKLIN. ANSWER TO SOME QUERIES OF MONSIEUR DUBOURG RESPECTING THE ARMONICA. London, Dec. 8, 1772. WHEN the glasses are ranged on the horizontal spindle, or, to make use of your expression, enfilés, and that each one is definitely fixed in its place,-the whole of the largest glass appears, at the extremity to the left;' the following one, nearly enclosed in the preceding one, shows only about an inch of its border, which advances so much further than the edge of the larger glass ;—and so, in succession, each glass exceeds the one containing it, leaving by this placement an uncovered border on which the fingers may be applied. The glasses do not touch one another, but they are so near as not to admit a finger to pass between them; so that the interior border is not susceptible of being rubbed. The finger is to be applied flat on the borders of the largest glasses, and on the borders of the smaller; but in part on the borders, and in part on the edges, of the glasses of an intermediate size. Nothing but experience can instruct with respect to this manutation, (fingering,) because the different-sized glasses require to be touched differently-some nearer the edge, and others farther from it. A few hours' exercise will teach this. B. F. ON FIRE. Craven Street, 1762. DID you ever see people at work with spades and pickaxes, digging a cellar? When they have loosened the earth perhaps a foot deep, that loose earth must be carried off, or they can go no deeper; it is in their way, and hinders the operation of the instruments. When the first foot of earth is removed, they can dig and loosen the earth a ! See Plate 1.-B. foot deeper.-But if those who remove the earth should with it take away the spades and pickaxes, the work will be equally obstructed as if they had left the loose earth unremoved. I imagine the operation of fire upon fuel with the assistance of air may be in some degree similar to this. Fire penetrates bodies, and separates their parts; the air receives and carries off the parts separated, which if not carried off would impede the action of the fire. With this assistance therefore of a moderate current of air, the separation increases, but too violent a blast carries off the fire itself; and thus any fire may be blown out, as a candle by the breath, if the blast be proportionable. But if air contributed inflammatory matter, as some have thought, then it should seem, that the more air the more the flame would be augmented, which beyond certain bounds does not agree with the fact. Some substances take fire, i. e. are kindled by the application of fire much sooner than others. This is in proportion as they are good or bad conductors of fire, and as their parts cohere with less or more strength. A bad conductor of fire not easily permitting it to penetrate and be absorbed, and its force divided among the whole substance, its operation is so much the stronger on the surface to which it is applied, and is in a small depth of surface strong enough to produce the separation of parts which we call burning. All oils and fats, wax, sulphur, and most vegetable substances, are bad conductors of fire. The oil of a lamp, burning at the top, may be scarce warm at the bottom; a candle or a stick of wood inflamed at one end, is cool at the other. Metals, which are better conductors, are not so easily kindled, though, when sufficient fire is applied to them to separate their parts, they will all burn. But the fire applied to their surfaces enters more easily, is absorbed and divided; and not enough left on the surface to overcome the cohesion of their parts. A close contact with metals will for the same reason prevent the burning of more inflammable substances. A flaxen thread, bound close round an iron poker, will not burn in the flame of a candle; for it must imbibe a certain quantity of fire before it can burn, i. e. before its parts can separate: but the poker, as fast as the fire arrives, takes it from the thread, conducts it away, and divides it in its own substance. Common fire I conceive to be collected by friction from the common mass of that fluid, in the same manner as the electrical fluid is collected by friction, which I have endeavored to explain in some of my electrical papers, and, to |