164 



A HISTORY OF 



ed to fall. After some months' confinement I] not, for some days, venture to leave his dun- 

 he was at last set free; but such was the ef- geori, but was obliged to accustom himself by 

 feet of the darkness upon him, that he could jj degrees to the light of the day. 



CHAPTER XXX. 



OF HEARING." 



AS the sense of hearing, as well as of sight, 

 gives us notice of remote objects, so, like that, 

 it is subject to similar errors, being capable 

 of imposing on us upon all occasions, where 

 we cannot rectify it by the sense of feeling. 

 We can have from it no distinct intelligence 

 of the distance from whence a sounding body 

 is heard ; a great noise far ofT, and a small 

 one very near, produce the same sensation ; 

 and unless we receive information from some 

 other sense, we can never distinctly tell whe- 

 ther the sound be a great or a small one. It 

 is riot till we have learned, by experience, 

 that the particular sound which is heard, is of 

 a peculiar kind ; then we can judge of the 

 distance from whence we hear it. When we 

 know the tone of the bell, we can then judge 

 how far it is from us. 



Every body that strikes against another pro- 

 duces a sound, which is simple, and but one 

 in bodies which are not elastic, but which is 

 often repeated in such as are. If we strike a 

 bell, or a stretched string, for instance, which 

 are both elastic, a single blow produces a 

 sound, which is repeated by the undulations 

 of the sonorous body, and which is multiplied 

 as often as it happens to undulate or vibrate. 

 These undulations each strike their own pe- 

 culiar blow; but they succeed so fast, one 

 behind the other, that the ear supposes them 

 one continued sound ; whereas, in reality, 

 they make many. A person who should, for 

 the first time, hear the toll of the bell, would 

 very probably be able to distinguish these 

 breaks of sound ; and, in fact, we can readily 

 ourselves perceive an intention and premis- 

 sion in the sound. 



In this manner, sounding bodies are of two 



1 This chapter is taken from Mr. Bullbn, except where 

 marked by inverted commas. 



kinds; those unelastic ones, which, being 

 struck, return but a single sound ; and those 

 more elastic, returning a succession of sounds; 

 which uniting together, form a tone. This 

 tone may be considered as a great number 

 of sounds, all produced one alter the other, 

 by the same body, as we find in a bell, or the 

 string of a harpsichord, which continues to 

 sound for some time after it is struck. A con- 

 tinuing tone may also be produced from a 

 non-elastic body, by repeating the blow quick 

 and often, as when we beat a drum, or when 

 we draw a bow along the string of a fiddle. 

 Considering the subject in this light, if we 

 should multiply the number of blows, or re- 

 peat them at quicker intervals upon the 

 sounding body, as upon the drum, for in- 

 stance, it is evident that this will have no ef- 

 fect in altering the tone ; it will only make 

 it either more even, or more distinct. But it 

 is otherwise, if we increase the force of the 

 blow: if we strike the body with double 

 weight, this will produce a tone twice as loud 

 as the former. If, for instance, I strike a table 

 with a switch, this will be very-different from 

 the sound produced by striking it with a cud- 

 gel. Hence, therefore, we may infer, that all 

 bodies give a louder and a graver tone, not 

 in proportion to the number of times they are 

 struck, but in proportion to the force that 

 strikes them. And, if this be so, those philo- 

 sophers who make the tone of a sonorous 

 body, of a bell, or the string of a harpsichord, 

 for instance, to depend upon the number only 

 of its vibrations, and not the force, have mis- 

 taken what is only an effect for a cause. A 

 bell, or an elastic string, can only be consi- 

 dered as a drum beaten; and the frequency 

 of the blows can make no alteration whatever 

 in the tone. The largest bells, and the longest 



