30 Dr. Charles J. B. Williams on the Production 



effect is obtained by connecting the sonorous solid, a tuning- 

 fork, for instance, with an extended surface of thin metal of 

 the same elasticity (2.). Such a metallic sounding-board 

 greatly increases the sound, and to the ear applied on it, does 

 so as much as a wooden one; but it is greatly inferior to this 

 in extent of excursive vibration, and consequently in the 

 volume of sound which it sends through the air (8.) ; besides 

 which it is capable of producing sounds of its own that injure 

 the purity of the original note. The superior power of wood 

 in this respect, as the medium of transfer, will now be sufficiently 

 clear. According to the experiments of Chladni, finely fibred 

 fir-wood conducts sound along its fibres with nearly the same 

 facility and velocity as steel. Such great molecular elasti- 

 city (2.) enables it to receive the slightest or most rapid vi- 

 brations uniformly from a vibrating solid, whilst from its light- 

 ness or small inertia (4.) these become sufficiently excursive 

 to take full effect on the air, (8.) ; and no new or interfering 

 sounds can be produced in the wood itself, because its want 

 of uniform density across the grain would absorb or destroy 

 any vibrations in a direction different from those of the sono- 

 rous bar or cord communicating with it. Messrs. Savart and 

 Wheatstone have well illustrated the influence of the form and 

 position of sounding-boards, with their effect of producing 

 within themselves, and with the contained air, vibrating sy- 

 stems ; but their material appears to have been in great mea- 

 sure overlooked. Examining the matter elementarily, we are 

 led to point out rigidity of loiigitudinal fbre, by which the 

 vibrations are equally and perfectly received from a sounding 

 cord or bar (2. and 8.) and lightness ofmass^ by which they 

 are made excursive and freely transferred to the air (4. and 7.), 

 as the two most essential qualities for the materials of sound- 

 ing-boards. These conclusions are quite in accordance with 

 the experience of musical instrument makers, and, perhaps, 

 may be useful in making this experience more rational and 

 certain. The same properties render light rigid wood a gobd 

 material for stethoscopes, which are intended to convey sounds 

 of various media in the most direct way to the ear. 



II. On the Sounds of single and repeated Strokes. 



10. Single blows, such as those of a hammer on a nail or 

 stone, are considered by Dr. Young and Sir John Herschel to 

 consist of a single impulse (4. and 6.), and not of succesive vi- 

 brations, and therefore to have no pitch. Hence they de- 

 scribe a succession of these, as in the striking of the teeth of 

 a cog-wheel against an object, as capable of producing musical 

 tones in the same way and at the same ratio as the vibrations 



