

Lord Rayleigh on Bells. 7 



it was concluded that none of them could be due to symme- 

 trical vibrations, as, till then, had been thought not un- 

 likely. 



Nothing further worthy of record was effected until last 

 year, when I obtained from Messrs. Mears and Stainbank the 

 loan of a 6-cwt. bell. Hung in the laboratory at a convenient 

 height, and with freedom of access to all parts of the cir- 

 cumference, this bell afforded a more convenient subject for 

 experiment, and I was able to make the observations by 

 which before I had been baffled. Former experience having 

 shown me the difficulty of estimating the pitch of an isolated 

 bell, I was anxious to have the judgment of the founders 

 expressed in a definite form, and they were good enough to 

 supply me with a fork tuned to the pitch of the bell. By my 

 harmonium the fork is d ,f . 



By tapping the bell in various places with a hammer or 

 mallet, and listening with resonators, it was not difficult to 

 detect 6 tones. They were identified with the following 

 notes of the harmonium * : — 



•', c", /"+, b'% d'», /"'. 



(4) (4) (6) (6) (8) 



As in the former case, the nominal pitch is governed by 

 the fifth component tone, whose pitch is, however, an octave 

 higher than that of the representative fork. It is to be un- 

 derstood, of course, that each of the 6 tones in the above 

 series is really double, and that in some cases the components 

 of a pair differ sufficiently to give rise to somewhat rapid 

 beats. The sign + affixed to f" indicates that the tone of 

 the bell was decidedly sharp in comparison with the note of 

 the instrument. 



I now proceeded to determine, as far as possible, the cha- 

 racters of the various modes of vibration by observations 

 upon the dependence of the sounds upon the place of tapping 

 in the manner already described. By tapping round a circle 

 of latitude it was easy to prove that for (each of the approxi- 

 mately coincident tones of) e ! there were 4 nodal meridians. 

 Again, on tapping along a meridian to find whether there 

 were any nodal circles of latitude, it became evident that 

 there were none such. At the same time differences of in- 

 tensity were observed. This tone is more fully developed 



* In comparisons of this kind the observer must bear in mind the 

 highly compound character of the notes of a reed instrument. It is 

 usually a wise precaution to ascertain that a similar effect is not produced 

 by the octave (or twelfth) above. 



