BELL, a well known machine, ranked by musicians among the musical instru ments of percussion.
The metal is usuallycomposed of three parts of copper and one part of tin. Its colour is greyish-white ; it is very hard, sonorous, and elastic. The greater part of the tin may be separated by melting the alloy, and then pouring a little water on it. The tin decomposes the water, is oxidised, and thrown upon the surface. According to Swedenberg, the English bell-metal is usually made from the sco ria of the brass gun foundry, melted over again. The proportion of tin in bell metal varies. Less tin is used for church bells than clock-bells ; and in small bells, as those of watches, a little zinc is added to the alloy. According to Gerbert, the conch of the East Indians is composed of tin and copper, in the same proportion as in bell-metal.
The constituent parts of a bell are, the body or barrel, the clapper on the inside, and the ear or cannon on which it hangs to a large beam of wood.
The sound of a bell consists in a vibra tory motion of its parts, much like that of a musical chord. The stroke of the clapper must necessarily change the figure of the bell, and of a round make it oval ; but the metal having a great de gree of elasticity, that part will return back again which the stroke drove far. thest off from the centre, and that even some small matter nearer the centre than before; so that the two parts, which be fore were extremes of the longest diame ter, do then become those of the short est : and thus the external surface of the bell undergoes alternate changes of fi gure, and by that means gives that tre mulous motion to the air, in which the sound consists.
M. Perrault asserts, that the sound of the same bell is a compound of the sound of the several parts of it ; so that where the parts are homogeneous, and the di mensions of the figure uniform, there is such a perfect mixture of all these sounds as constitutes one uniform, smooth, even sound, and the contrary circumstances produce harshness. To confirm this, he observes the different tone of the bell, according to the part of it that is struck ; and yet, strike it where you will, there is a motion of all the parts. He therefore
considers bells as composed of an infinite number of rings, which have different tones, according to their different dimen sions, as chords of different lengths have, which, when struck, the vibrations of the parts immediately struck determine the tone, being supported by a sufficient number of consonant tones in other parts.
It has been found by experience, that bells are heard farther, if placed on plains, than on hills, and still farther in vallies than on plains ; the reason of which may be easily comprehended, by considering, that the higher the sono rous body is, the medium is the rarer, and consequently receives the less im pulse, and the vehicle is the less proper to convey it to a distance.
The bell-founders distinguish two sorts of proportions, viz. the simple and the re lative. The simple proportions are those which ought to be between the several parts of a bell, and which experience has shewn to be necessary towards rendering is sweetly sonorous. The relative pro portions are those which establish a re quisite relation between one bell and an other, so that their combined sounds may effect a certain determined harmony.
The use of bells is very ancient, as well as extensive. We find them among the Jews, Greeks, Romans, Christians, and Heathens, variously applied, as on the necks of men, beasts, birds, horses, sheep ; but chiefly hung in buildings, either religious, as in churches, temples, and monasteries ; or civil, as in houses, markets, baths; or military, as in camps, and frontier towns.
When they were first invented, or who introduced them into the Christian church, is not at present known : but it appears that they were employed in the eastern church in the ninth century, when Urcus Patriciacus, Duke of Venice, made a present of a set to Michael, the Greek emperor, who built a tower to the church of &meta Sophia, in which to hang them.