Lord Rayleigh on Bells. 5 



in pitch to the tone under examination is chosen and tuned by 

 advancing the finger across the aperture. Without the security 

 afforded by resonators, the determination of the octave is in 

 my experience very uncertain. Thus pure tones are often 

 estimated by musicians an octave too low. 



Some years ago I made observations upon the tones of 

 various glass bells, of which the walls were tolerably thin. 

 A few examples may be given : — 



I. 



II. 

 III. 



c'% h". 



f% w. 



The value of n for the gravest tone is 2, for the second 3, 

 and for the third I. On account of the irregular shape and 

 thickness only a very rough comparison with theory is 

 possible ; but it may be worth mention that for a thin uniform 

 hemispherical bell the frequencies of the three slowest vibra- 

 tions should be in the ratios 



1 : 2-8102 : 5*4316 ; 



so that the tones might be 



c , f% f> approximately. 



More recently, through the kindness of Messrs. Mears and 

 Stainbank, I have had an opportunity of examining a so- 

 called hemispherical metal bell, weighing about 3 cwt. A 

 section is shown in fig. 1. Four tones could be plainly heard, 



e\>, f% e", b", 

 the pitch being taken from a harmonium. The gravest tone 



Fig. 1. 



has a long duration. When the bell is struck by a hard 

 body, the higher tones are at first predominant, but after a 

 time they die away, and leave e\> in possession of the field. 

 If the striking body be soft, the original preponderance o( the 



higher elements is less marked, 



