INFLUENCE OF SUSPENSION ON WATCH. 369 



of metal, or a common bell, are incommensurable. 

 Hence these bodies cannot give any true musical 

 sound other than a pure and simple harmonic note. 

 A large sheet of metal, or a gong, or a drum, when 

 struck, produces an infinite number of discordant 

 notes sounding simultaneously (hence used for 

 " music of demons " in lyric theatres !). But in 

 the drum, the gravest of the fundamental notes 

 predominates more decidedly, than does any one of 

 the fundamental notes in the two other cases ; and 

 thus a drum gives a nearer approach to a true 

 musical sound than a sheet of brass or a gong. 



An excellent illustration of the general 

 theory is presented by the double pendulum 

 one pendulum hung from the weight of another. 

 If we admit only vibrations in one plane, the 

 system has two degrees of freedom to move. 

 The determinant equation becomes a quadratic 

 with two roots, necessarily unequal. The mathe- 

 matics need not be given here ; but may be 

 advantageously worked out as an exercise by the 

 dynamical student. In the graver fundamental 

 mode the two cords deviate always in the 



VOL. II. B B 



