

Lord Bayleigh on Bells. 9 



tone, g" ! , was but imperfectly heard, and no investigation could 

 be made of the corresponding mode of vibration. 



In the specification of pitch the numerals following the 

 note indicate by how much the frequency for the bell dif- 

 fered from that of the harmonium. Thus the gravest tone 

 e'\> gave 2 beats per second, and was flat. When the number 

 exceeds 3, it is the result of somewhat rough estimation and 

 cannot be trusted to be quite accurate. Moreover, as has 

 been explained, there are in strictness two frequencies under 

 each head, and these often differ sensibly. In the case of 

 the 4th tone, b"\) — b" means that, as nearly as could be judged, 

 the pitch of the bell was midway between the two specified 

 notes of the harmonium. 



The sounds of bells may be elicited otherwise than by 

 blows. Advantage may often be taken of the response to 

 the notes of the harmonium, to the voice, or to organ-pipes 

 sounded in the neighbourhood. In these cases the subsequent 

 resonance of the bell has the character of a pure tone. Per- 

 haps the most striking experiment is with a tuning-fork. A 

 massive e'\) (V on the c' = 256 scale) fork, tuned with wax, and 

 placed upon the waist of the Amp ton bell, called forth a 

 magnificent resonance, which lasted for some time after re- 

 moval and damping of the fork. The sound is so utterly 

 unlike that usually associated with bells that an air of mystery 

 envelops the phenomenon. The fork may be excited either 

 by a preliminary blow upon a pad (in practice it was the bent 

 knee of the observer), or by bowing when in contact with 

 the bell. In either case the adjustment of pitch should be 

 very precise, and it is usually necessary to distinguish the 

 two nearly coincident tones of the bell. One of these is to 

 be chosen, and the fork is to be held near a loop of the cor- 

 responding mode of vibration. In practice the simplest way 

 to effect the tuning is to watch the course of things after the 

 vibrating fork has been brought into contact with the bell. 

 When the tuning is good the sound swells continuously. 

 Any beats that are heard must be gradually slowed down by 

 adjustment of wax, until they disappear. 



Observations upon the two bells in the laboratory having 

 settled the modes of vibration corresponding to the five 

 gravest tones, other bells of the church pattern can be suf- 

 ficiently investigated by simple determinations of pitch. I 

 give in tabular form results of this kind for a Belgian bell, 

 kindly placed at my disposal by Mr. Haweis, and for the five 

 bells of the Terling peal. For completeness' sake the Table 

 includes also the corresponding results for the two bells 

 already described. 



