CHAP, n.l MUSICAL INSTRUMENTS. 125 



II. BELLS AND CAKILLONS on CHIMES. 



Vibrating plates need not necessarily be flat, of rectangular or 

 discoidal form, they may be also shaped into hemispherical or ellip- 

 soidal forms, as in bells, which are put to the most varied uses. 



Bells of all kinds are most frequently used for giving signals, 

 whether in every-day life or in works, railways, ships, etc. They 

 are made of all sizes, and the notes which they give out generally 

 are a composition of harmonic sounds produced by the parts of the 

 sonorous body divided by the nodal lines. The deepest or funda- 

 mental note is that which most strikes the ear, and the mixture 

 of the sharpest or highest notes gives to the bell the tone which 

 is peculiar to it, and which the ear, although it can scarcely define 

 it, easily recognizes. 



Church bells have from time immemorial an almost traditional 

 form, of which Figs. 79 and 80 represent a section and general 

 appearance. The Japanese bell represented in Fig. 81 has evi- 

 dently a very different form from that of European church bells. 



In these, the outline and thicknesses of the metal at different 

 heights of the bell are calculated so that the deepest sound pro- 

 duced by the vibiation of the extreme edge or rim is an octave 

 lower than the note of the head. Diderot writes that "The dia- 

 meter of the head, when only half that of the rim, will sound the 

 octave above that of the latter. The sound of a bell is not a simple 

 sound, but is composed of different sounds produced by the different 

 parts of the bell, in which the fundamental ought to absorb the 

 harmonics, as it is said to do in the organ ; if the perfect harmony 

 c, E, G, be sounded together, the higher G, E, G, B, G, B, I) are 

 sounded at the the same time ; nevertheless only c, E, G are heard 

 at a distance, or perhaps only c. The ratio of the height of the 

 bell to its diameter is as 12 to 15, or in the ratio of the funda- 

 mental to the major third: whence it is concluded that the note 

 of the bell is principally due to the vibration of its rim, as funda- 

 mental, into that of the crown, which gives the octave, and that of 

 the height, which gives the third. But it is evident that these 

 dimensions are not the only ones which give out tones more or 

 less deep ; in the entire bell there is no part of the circumference 



