ACOUSTICAL INSTRUMENTS. 103 



ton. Then come a series of experiments by Hamilton in conjunc- 

 tion with Hermann Smith, in which the reed tone is regarded apart 

 from the string, and produced as an organ note, the string's 

 functions analysed, and the string replaced by other bodies linked 

 to the reed, and reacting upon it, and the mode of transmission 

 to solid bodies investigated and illustrated. The discovery that 

 reeds can obtain a sympathetic resonance from solid bodies leads 

 to a new field of experiment. Reverting to experience, it is 

 evident that besides the familiar instances of violin and organ- 

 pipe, there exists in solid bodies the same power of strengthening 

 and reacting upon a source^of vibration. 



We often hear organ-tones accidentally imitated in a large 

 building. Thus the dragging of a bench across a marble floor 

 will awake a grand violone sound ; the shifting of a chair often 

 gives rise to a clear trumpet tone ; and sometimes the shivering 

 of a great door as it slowly closes by its own weight rivals the 

 note of the deepest pedal pipes. Such sounds cannot at once be 

 discriminated from organ notes, but their want of continuity and 

 of steady pitch robs them of all elements of grandeur, and reduces 

 them to the level of noises. 



In the large collection of apparatus contributed by Mr. Baillie 

 Hamilton, we can estimate the chances of recovering to our use 

 these sources of sound, necessarily ranking among their number 

 the ^Eolian sounds, and sounds which have been often heard and 

 enjoyed in nature, but which have not as yet been harmonised or 

 controlled. 



In the revival of mechanical methods, as applied to the deter- 

 mination of sound, which has taken place within the last century, 

 an early instrument for computing vibrations continues to be of 

 service, namely, Savart's toothed wheel ; the teeth of which, 

 rotating with a measurable velocity, are made to impinge on a 

 resonant body, and the pitch of the note produced is compared 

 with a standard. 



But the tension and division of strings were also early utilised 



