198 Sir G. S. Mackenzie, Bart., on the 



risy as light and heat, and to have become content with the 

 rather unsatisfactory conclusion of its being mere mechanical 

 action. Such a conclusion, however, does not afford suffi- 

 cient ground for altogether ceasing to observe the phenome- 

 na of sound, and the circumstances under which it is made 

 known to the sense of hearing. 



Motion is necessary to the evolvement of everything that 

 we know by means of our senses ; and there does not appear 

 to be any well-defined meaning attached to the word mecha- 

 nical, in reference to action. Motion being common to all 

 action, and being regulated by force, I apprehend that the 

 only distinction meant, in using such terms as mechanical 

 and chemical, refers to the causes and results of action, and 

 not to any variation in action itself. That sound is a result 

 of mechanical action (using that term in contradistinction to 

 action of any other kind), does not establish that it is not 

 something sui generis. Sound is the result of chemical and 

 electrical action also ; and Sir John Herschel's definition, on 

 that account, is confined to the result of every kind of action, 

 viz., motion. " Sound," he says, " consists in a motion of 

 the air itself, communicated along it by virtue of its elasti- 

 city." The expression, " a motion," is indefinite, and gives 

 no information. It is, besides, incorrect, inasmuch as it in- 

 fers the existence of more kinds of motion than one, while 

 more than one does not exist. Motion is one ; and its being 

 capable of variation in direction, circumscription, and velo- 

 city, effects no change. The fact, however, that sound is 

 produced by a motion of the air itself, communicated along 

 it by virtue of its elasticity, is true. But sound, did it con- 

 sist of a motion of the air itself, could not consist of any- 

 thing else. Nevertheless, we may as truly say, that sound 

 consists of a motion in hydrogen, in oxygen, in nitrogen, or 

 in any gaseous matter, seeing that from all of them sound 

 proceeds under similar circumstances, with more or less in- 

 tensity, according to their density.* 



* Dr George Wilson recently exhibited to the Royal Scottish Society of 

 Arts, the sounds produced by the passage of the electric spark through various 

 gases ; and the result confirmed what i s stated above, and in subsequent parts 

 of this paper. February 22, 1847. 



