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through the line with greater velocity than the impinging 

 marble would travel through the like space, and that the 

 furthest or external marble is driven off with nearly the 

 same velocity as the impinging one had acquired, the inter- 

 mediate ones remaining apparently at rest, (at least as 

 regards the first impulse.) This I will beg to term motion 

 by impulse, or impulsive motion. 



It is easily perceived that sound is not the actual pro- 

 gressive motion of the whole body of air affected by it, 

 for the motion of sound is not generally accompanied by 

 apparent force, (except in some extreme cases, as when 

 windows are broken by the sound of cannon) ; and as I 

 am not aware that any other species of motion, other than 

 wave motion or impulsive motion, or one of these combined 

 with a small amount of actual motion, have been suggested 

 as the motion of sound, we will endeavour to form some 

 opinion whether the supposition of wave motion, or of pro- 

 gressive motion, is the most probable, and which, with the 

 least difficulty, supplies the explanations required by the 

 known phenomena of sound. 



It is, I believe, a very general opinion that the progression 

 of sound is by waves ; this, perhaps, is from the force of 

 early impression, from the comparison of the formation of 

 sound to the waves of water, into which a stone has been 

 thrown. This simple comparison may give a moderately 

 good idea of the manner in which sound radiates from a 

 centre, but I cannot agree that it is applicable any further. 



Again, it appears that in the earlier age of experimental 

 philosophy, when dogmatical opinions were readily received 

 with little examination, sound was considered to be so 

 decidedly undulatory in its nature, that it supplied an 

 argument by analogy that light was of a similar nature. 



The undulatory motion of the segments of a goblet or a 

 plate, and the waves produced on the surface of liquid placed 



