M. Dobereiner of Jena, conceives that the pheno menon now described is an effect of an electromag netic action; and he proposes to try if the brass wire would not sound when it communicates at its extre mity with an energetic electrometer. See Brewster's Journal of Science, vol. iii.
9. Description of the Harmonica The name harmonica has been given to a combina tion of musical glasses, having their sizes so adjusted to one another, as to give the different octaves of the sounds which are commonly employed in music. When the glasses, however, have different thick nesses, though their size and their mode of vibrating be the same, they give sounds proportional to their thicknesses. It is necessary therefore to choose glasses whose thickness is equal throughout the whole of their surface. Glasses must also be chosen which have a clear and agreeable sound, and which can be easily put into vibration. Thin glasses with a high stalk have been commonly employed, or cups of glass or porcelain. When glasses with stalks are used, they must be placed vertically beside one another, and in the order of the notes of the different octaves. They are then tuned by pouring more or less water into them, which depresses the sound more and more. When the glass vibrates, the water is also thrown into a. state of vibration, as may be seen by the ripples which are formed on its surface. Other fluids may be employed, but the quantity poured in will vary with their specific gravity. If mercury is put into a very large vessel, the edge of which is rubbed by the bow of a fiddle, the ripples on the surface of the mer cury are very large, and are kept up for a much longer time. In place of using a bar, it is customary to apply the wetted finger. In this way the sound produced is the same as that which produces the figure shown in Plate CCCCLXXXIII. Fig. 10.
In the harmonica thus constructed, there is neces sarily a perceptible interval between the production of the different sounds. In order to remedy this disad vantage, the cylindrical or rotatory harmonica has been constructed. It consists of seven glass cups of a proper size, having a horizontal axis passing through their centre, and to which is given an uniform and continuous rotatory motion. A belt or board of leather kept constantly wet, is extended over all the glasses in the direction of their length, its two extremities being firmly fixed, in order that the rotatory motion of the glasses may not drag the leather along with them. In order to bring out a note from any particular glass, we have only to press the leather upon the glass, and the intensity of the sound may be made to vary with the degree of pressure applied. Still, however, a perceptible interval of time elapses before the motion of vibration is communicated to each glass; so that this instrument is only suited to perform pieces of music, the movement of which is very slow.
M. Grenie has made great improvements on the harmonica. Having procured cups of glass of the same kind, and of dimensions suited to the musical scale -which he wishes to embrace, he perforates them all at their summit or bottom, at the place where they are to be fixed on the cylinder. He then takes spheri cal moulds, and grinds down the glasses upon a turn ing lathe both on the inside and on the outside, till they are exactly of the same thickness. He next
grinds them gradually down on their rim perpendicu lar to their axis, until when placed on the cylinder they give out the exact sound which is wanted, which is done by comparing the sounds with those of a well tuned organ. The same process is applied to every one of the glasses; so that an instrument fitted up in this way is in every respect preferable to those made in the ordinary manner.
M. Biot, from whom we have taken the preceding description of the harmonicon, remarks that persons of a nervous temperament are deeply affected with the tones of this instrument.
10. Description of the illelodion.
This musical instrument was invented about twelve years ago by M. Dietz, a German, and he has given it the name of melodion from the sweetness and harmo ny by which it is characterized. We had the. good fortune to hear the instrument in actual use at Geneva in 1814, a short time after its invention, and we are surprised that it has not come into more general use. This instrument was so complete that it imitated a whole band of music, and its tone had a sweetness and a force which we have never heard equalled. The only printed notice that we have seen of it is that given by Biot, which we shall follow. The melodion em braces five octaves, the different notes of which are produced by the vibrations of metallic rods* of the same material, but of unequal lengths, fixed at one end and free at the other. The vibratory motion was com municated to them by a metallic cylinder or wheel, which the performer turned by means of a pedal. The surface of the cylinder, however, is not applied direct ly against the rods. Each of the rods carries at its free extremity and at right angles to its direction, a narrow and thin plate of copper screwed to it, and hav ing its surface covered with a small piece of felt im pregnated with colophane. This small band being placed near the circumference of the revolving cylin der is made to descend by touching the key which be longs to it till it comes into contact with the revolving cylinder and gives out its sound. The sound contin ues as long as the plate of copper is pressed against cylinder, and it may be increased or softened by in creasing or diminishing the motion of rotation of the cylinder. The moment the finger is taken from the key the plate of copper quits the cylinder and rests upon a soft body which instantly makes its vibrations cease.
As the sounds of metallic rods are directly propor tional to their thicknesses and reciprocally to their lengths, the rods must be lengthened and diminished in diameter in order to produce grave sounds. In this case it is difficult to elicit their fundamental sound, and when the flexibility of the rods is great the vibra tions are uncertain. M. Dietz has in a very ingenious manner remedied these disadvantages. He loads the metallic rods with small metallic discs perforated in the direction of their diameter, so that they can be kept by friction on any part of the rod. By sliding these discs along the rod, the intonation of the rod varies with the position, and the sound becomes more grave in proportion as these discs increase in magnitude. This double effect enabled him to obtain very grave sounds with very stiff rods, and to regulate the tuning of the instrument with the greater facility.