274 EIGHTEENTH CENTURY. PT. in. 



principle as the quiet lines of water in the glass, but their ex- 

 planation is rather complicated. The first two are the most 

 simple; in them the squares marked a a are always bending 

 upwards when the other squares b b are bending downwards, 

 and the lines between these four squares are therefore motion- 

 less, and form nodes. In our day Sir Charles Wheatstone 

 has analysed all these vibrations, and shown mathematically 

 why they assume the forms which Chladni produced. 



Chladni did not only discover the way in which plates 

 vibrate : he also worked out most carefully the whole theory 

 of musical sound, and left behind him a 'Treatise on 

 Acoustics,' which is still of very great value. He .also in- 

 vented two musical instruments, the euphone and the 

 clavicylinder, which are, however, no longer in use. The 

 manner of his death was somewhat singular. At an evening 

 party held at the house of one of the professors of the 

 Breslau University, he was speaking of sudden death as a 

 happy thing when happening to a man whose work was 

 done. At eleven o'clock he went home, and the next 

 morning he was found dead in his chair; his watch, which 

 he must have been in the act of winding, having fallen open 

 at his feet. He had died of apoplexy. 



As we shall not be able to return again to the subject of 

 sound, it may be well to state here, that great advances have 

 been made in it during the nineteenth century, especially by 

 Professor Helmholtz, who has worked out the theory of 

 musical sounds most completely, and has also explained very 

 fully the .structure of the ear, and the manner in which the 

 vibrations affect it. 



Chief Works *w.r/,ta/. Sauveur, 'Memoires ; Acad. des Sciences,' 

 1701-1707; Fetis, 'Biog. des Musicians;' Helmlioltz, ' Sensations of 

 Tone;' Tyndall, 'On Sound;' Chladni, " Die Akustik ;' Chladni, 

 * Endeckuiiiieu iiber die Theoiie des Klanges ;' Acad, des Sci. 1786. 



