The name given to a musical instrument invented by Dr. Franklin, in which the tones are produced by friction against the edges of a series of glasses. The glasses are blown as near as possible into the form of hemispheres, having each an open neck or socket in the middle. The thickness of the glass near the brim is about one-tenth of an inch, but thicker as it cornea nearer the neck, which, in the largest glasses, is about an inch deep, and an inch and a 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 in diameter, and the smallest three inches. Between these there are twenty-three different sizes, differing from each other a quarter of an inch in diameter. The glasses being chosen, and every one marked with a diamond the note for which it is intended, 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 piano-forte or harpsichord.

The largest glass in the instrument is C, a little below the reach of a common voice, and the highest G, including three complete octaves; and they are distinguished by painting the apparent parts of the glasses within side, every semitone white, and the other notes of the octave with the seven prismatic colours; so that glasses of the same colour (the white excepted) are always octaves to each other. The glasses being tuned, they are to be fixed on a round spindle of hard iron, an inch in diameter at the thickest end, and tapering to a quarter of an inch at the smallest. For this purpose the neck of each glass is fitted with a cork, projecting a little without the neck; these corks are perforated with holes of different diameters, according to the dimensions of the spindle in that part of it where they are to be fixed. The glasses are all placed one within another, the largest on the biggest end of the spindle, with the neck outwards; the next in size is put into the other, leaving about an inch of its brim above the brim of the first; and the others are put on in the same order. From these exposed parts of each glass the tone is drawn by laying a finger upon one of them as the spindle and glasses turn round.

The spindle thus prepared is fixed horizontally in the middle of a box, and made to turn on brass gudgeons at each end. A square shank comes from its thickest end through the box, on which shank a fly-wheel, to equalize the motion, is fixed. This wheel is made of mahogany, eighteen inches in diameter, and pretty thick, to conceal near its circumference about 25lbs. of lead. An ivory pin is fixed to the face of this about four inches from the axis, and over the neck of this pin is put the loop of a string from a treadle, by which the machine is put in motion. The whole is put in a neat case, and stands on a frame with four legs. The case is three feet long; eleven inches wide at the largest end, and five at the smallest; it is made with a lid, which opens at the middle of its height, and turns up by back hinges: the instrument is played upon by sitting before the middle of the set of glasses, 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 greasiness; a little fine chalk 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. " The advantages of this instrument are," says Dr. Franklin, " 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."