Lesson xvm.J SOUND. 99 



Experiments on the air-pump prove to us, that 

 without the assistance of air, sounds cannot be 

 produced : they also evince, that the nature of 

 sounds depends entirely upon a certain motion of 

 the aerial particles. This motion is a pulsive or 

 vibratory one, carrying these particles forward 

 and backward through the very same space : and 

 it results from, or depends upon, the spring or 

 elasticity of the air. It is by means of this power 

 that, when any one particle is by any cause urged 

 forward, it must necessarily propel the particle 

 next before it : this second particle, in the same 



vague, indefinite ones, which are now in use. What is the in- 

 formation we can obtain from casting our eyes upon the cha- 

 racters f > T> T> , &c. ? Why truly, no more than can be learn- 

 ed from reckoning up the Crotchets, Minims, Quavers, &c. in 

 the first complete bar in the tune. The characters for the 

 several rates of common time ; and the terms Adagio, Largo, 

 Allegro, Presto, &c. &c. are also of very little avail in ascer- 

 taining with precision the point the musician wishes to dis- 

 cover. Every composer of musical airs, &c. would be of real 

 iervice to the practitioner, if he would point out the absolute 

 rate at which his music is to be performed : this would be no 

 difficult task ; as he would only have to mention the length of 

 a pendulum which would make one complete vibration in the 

 time that part of a bar called a beat was performing. Thus, 

 for instance, suppose I set a tune in triple time, and wish to 

 have each bar performed in a second and a half, the cha- 

 racter I must make use of is iV for from this it might be con- 

 cluded that there were three beats in a bar, and each of these 

 beats must be performed in the time a pendulum 10 inches 

 long made one vibration. 



To explain this method clearly, much more room is requisite; 

 but the present would not be a proper place for it : however, 

 Jthosc who understand what improvement i: intended, from 

 this short account, will, I hope, excuse me for exhorting 

 them to use their best endeavours to make it general. 



F 2 manner, 



