MONOCHORD, in music, an ancient instrument, or machine, so called, be cause it is furnished with only one string._ Its use is to measure and adjust the ratios of the intervals, which it effects by the means of moveable bridges, calculated to divide the chord at the pleasure of the performer. The monochord was regarded by the ancients as the only means of form ing the ear to the accurate perception, and the voice to the true intonation those minute aml difficult intervals which were then practised in melody. Lord Stanhope, who has employed much time on the subject of music, has described a new monochord, of which the following is his Lordship's account.
1. The wire is made of steel, which does not keep continually lengthening, like brass or iron. 2. The whole wire forms one straight horizontal line, so that the moveable bridge can be moved with. out altering the tension of the wire ; which is not the case when the wire pulls downwards on the bridges. S. The ends of the wire are not twisted round the two stout steel pins that keep it stretched ; but each end of the wire is soft soldered in a long groove formed in a piece of steel, which goes over its corresponding pin. 4. One of these two steel pins is strongly fastened by a brass slider, which is moved by means of a screw with very fine threads, this screw having a large micrometer head minutely divided on its edge, and a corresponding nonins ; whence the tension of the wire may be very exactly adjusted. 5. A slider is fixed across the top of the moveable bridge, and is moved by means of an other screw with very fine threads. 6. The slider is adjusted to the steel rod or scale, by means of mechanical contact against projecting pieces of steel firmly fixed on that steel scale, at the respective dis tances specified in the monochonl table. 7. Each bridge carries a metallic finger, which keeps the wire close to the top of such bridge, while the remainder of the wire is made to vibrate. 8. The vibra
tions of the wire are produced by touch. ing it with a piece of cork with the same elastic force, and always at the distance of one inch from the immoveable bridge. The Stanhope monochord, though very in constructed, is in some respects thought inferior to the monochord con trived by Mr. Atwood. In this gentle man's apparatus the string hangs verti cally, its tension being regulated by a weight suspended at its lower extremity, a little below the place where the string comes into contact with a fixed pulley ; the length of the string is terminated at top by a horizontal edge ; the other point of termination, which in the com mon monochords, as well as in many mu sical instruments, and in the Stanhope monochord, is a bridge over which the string is stretched, is in this construction effected by two steel edges vertically placed, that are capable of approaching, or of receding from, one another, like the cheeks of a vice : these, being fixed on a frame worked by micrometer screws, can be easily moved in the vertical direc tion, so as to alter the length of the string in any desired proportion : these edges are separated occasionally by a spring in order to let the string pass freely through, when its length is altered, and are closed again, so as to press the string slightly, when that length is pro perly adjusted. By means of this con struction the alteration of the tending force, by the application of bridges, &c. is wholly avoided. The scale placed under the string of this monochord is divided into 100 equal parts, and each of these by a micrometer screw into 1000 equal parts ; so that, by the aid of a microscope and a proper index, the length of a given part of the string may be adjusted on the monochord true to the TWOIS dth part of its whole length.
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