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



Association an attempt to give a greater precision to our 

 ideas on this subject, in a few considerations which have re- 

 sulted from the study of acoustics in connexion with its appli- 

 cation to the distinction of diseases ; and until they shall be 

 confirmed by more competent authorities, I would advance 

 the following remarks as inquiries, rather than as absolute 

 assertions. 



I. On the Nature and Transfer qfsonm'ous Vibrations. 



1 . It is generally said in works on acoustics, that solids are 

 good conductors of sound; but this expression requires quali- 

 fication, for the power of bodies to transmit sound is not ab- 

 solute, like the properties of conducting heat or electricity, 

 but relative to the matter and form of the body from which 

 the sound directly proceeds. Thus, the ticking of a watch is 

 transferred to the ear perfectly through the longest piece of 

 timber, but the sound of the voice or of a flute passes much 

 more readily through the air*. As this subject is one of great 

 importance in practical acoustics, and as it does not appear to 

 have been developed to the extent of which it is capable, 

 I may be permitted to enter a little minutely into the nature 

 and progress of the motions constituting sound in various 

 bodies. 



t2. All matter is susceptible of sonorous vibrations, and as 

 a general rule, it may be stated that this susceptibility or ca- 

 pacity is in proportion to the strength and uniformity of the 

 molecular elasticity in the matter. By molecular elasticity is 

 meant that force by which the molecules of a body are held 

 at a certain distance from each other, and resist any effort to 

 displace them from it. Thus, glass and steel may be said to 

 possess molecular elasticity in a powerful degree, because any 

 external impulse is instantaneously communicated from par- 

 ticle to particle throughout their whole mass, and it is not 

 lost or broken by the yielding or displacement of the molecules 

 at the point struck. Air and other fluids, on the other hand, 

 cannot be readily thrown into vibrations, unless the impulse 

 be very forcible, or applied to some extent of surface, by 

 which it becomes communicated to many particles at once. 



3. Sound has been defined by Dr. Young and others, as 



* Thu« in Mr. Wheatstone*8 beautiful experiments with the " Enchanted 

 Lyre" he could not succeed in transmitting, by any contrivancey the sound of 

 the voice or a flute through a solid conductor without very great loss in the 

 intensity of the sound; whereas the notes of solid cords or wires passed so 

 little inipaired by the transfer as to produce the magical effects of the in- 

 strument just mentioned. (See the last Numbers of the Journal of the 

 Royal Institution.) It is hoped that the succeeding remarks in the text will 

 explain the causes of these differences. 



