PHYSICS. NINETEENTH CENT. SOUND. 



539 



variations of the mode of treatment (see Fig. 256). Chladni, in 1787, 

 published a memoir describing the vibrations of a round and a square 

 plate. He afterwards figured and described several hundred forms 

 obtained with plates of various shapes. 



Chladni devised a very simple method of counting the number of 

 vibrations corresponding with each note. He took a strip of iron or of 

 brass about half an inch wide, one-twelfth of an inch thick, and of such a 

 length that when one end of the strip was fixed in a vice, the vibrations 

 were sufficiently slow to be counted by the eye, a task which is not 



FIG. 257. 



difficult if they do not exceed eight per second. Taking such a length 

 of the strip that its vibrations were, say, four per second, the number 

 which would be counted if the length of the strip were made one- 

 half, would be sixteen that is, four times as many, and so on ; the 

 law, as established from mechanical considerations, being that the 

 number of vibrations are inversely as the square of the length. It was 

 thus perfectly easy to deduce the number of vibrations corresponding 

 with any length of the strip. In practice, however, there were found 

 to be circumstances attending this method of experimentally ascer- 

 taining the number of the vibrations which detracted much from its 

 theoretical accuracy. It was difficult, for instance, to obtain a strip 

 of metal of absolutely the same thickness and elasticity throughout its 

 entire length, and the experimenter would never be certain that no 

 play of the strip could occur between the jaws of the vice used for 

 fixing it. 



