146 Mr TREVELYAN on the Vibration of Heated Metals. 



That the tremulous metal causes no sound when the two sur- 

 faces are smoothly polished, as there is then no opening for the 

 stream of air ; and, %dly, that the current of air occasions no 

 sound when there is no vibration of the solid, seeing no sound is, 

 heard when a heated bar of lead rests upon a block of the. same 

 metal, and when no vibration is visible. 



I shall not lengthen this paper by attempting to explain the 

 disposition of the apparatus to yield notes of particular intona- 

 tion. 



