1857.] Prof. Tyndall on Acoustic Experiments, 441 



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WEEKLY EVENING MEETING, 

 Friday, June 5. 



The Duke op Northumberland, K.G. F.R.S. President, 

 in the Chair. 



John Tyndall, Esq. F.R.S. 



rROFESSOB OF NATURAL PHILOSOPHY, R,T. 



On M. Lissajous* Acoustic Experiments. 



The speaker briefly noticed the physical cause of musical sound ; 

 referring to the bell, the tuning fork, the tended string, &c., as 

 sources of vibration. The propagation of impulses through the 

 atmosphere to the tympanum was illustrated by causing a brass rod 

 to vibrate longitudinally : a disk was fixed to the end of the rod 

 perpendicular to its length, and this disk, being held several feet 

 above a surface of stretched paper on which sand was strewn, 

 communicated its motion through the air to the paper, and pro- 

 duced a complex nodal figure of great beauty. Optical means 

 had been resorted to by Dr. Young, and more especially by Mr. 

 Wheatstone, in the study of vibratory movements. M. Lissajous 

 had extended and systematised the principle; and had exhibited 



