358 HISTORY OF ACOUSTICS. 



the discovery and classification of the phenomena ; 

 the detection of their formal laws; and, finally, 

 the explanation of these on mechanical principles. 

 We must speak very briefly of what has been done 

 in these ways. The facts which indicate Nodal Lines 

 had been remarked by Galileo, on the sounding- 

 board of a musical instrument; and Hooke had 

 proposed to observe the vibrations of a bell by 

 strewing flour upon it. But it was Chladni, a 

 German philosopher, who enriched acoustics with 

 the discovery of the vast variety of symmetrical 

 figures of Nodal Lines, exhibited on plates of regu- 

 lar forms, when made to sound. His first investiga- 

 tions on this subject, Entdeckungen uber die Theorie 

 des Klangs, were published in 1787: and in 1802 

 and 1817 he added other discoveries. In these 

 works he not only related a vast number of new 

 and curious facts, but in some measure reduced 

 some of them to order and law. For instance, he 

 has traced all the vibrations of square plates to a 

 resemblance with those forms of vibration in which 

 there are Nodal Lines parallel to one side of the 

 square, and to the other ; and he has established a 

 notation for the modes of vibration founded on this 

 classification. Thus, 5-2 denotes a form in which 

 there are five Nodal Lines parallel to one side, and 

 two to another; or a form which can be traced 

 to a disfigurement of such a standard type. Savart 

 pursued this subject still further; and traced, by 

 actual observation, the forms of the Nodal Surfaces 



