10 Mr Weber on the Polarisation of Sound. 



Table of the Changes of Position in which the Tone Vanishes, 

 by changing the proportion of the breadth of the branch to 

 its thickness. 



Angle of the Greatest 



Pitchpipe Position at Number Deviation 



which gives Breadth of Thickness of Distance of which the of Experi- of the Ex- 

 the sound «. the Branches, the Branches, the Plates. Sound Va- meats. periments 



nishes. from the 



Mean. 



No. 1. 3.5 lines. 1.1 lines. 4.8 lines. 144^ 8 s£ 



No. 2. 2.9 1.75 2.4 1394 8 4 



No. 3. 2.5 1.5 4.1 134 10 4 



With a pitchpipe whose branches were equilateral triangular 

 prisms, the angle of the position in which the tone vanished, with 

 the side of the pitchpipe parallel to its breadth, is 124i°. These 

 facts will appear more distinct in following some experiments 

 of the celebrated philosopher Dr Chladni. After this accom- 

 plished acoustician proved the truth of what has been already 

 stated, he proceeds to call our attention to the propriety of de- 

 nominating these experiments Polarisation of Sound, rather 

 than Wheatstone's Experiments ; and devised this ingenious 

 mode of satisfying with ease a whole assembly of these facts. 



As M. Savart first called our attention to the strengthening 

 of sounds by the mere presence of any organ-pipes tuned to 

 accord, and as, by means of Chladni's instrument, in which iron 

 rods gave the tone, much depended on the accurate tuning of 

 the rods, Chladni has likewise made use of this means of aug- 

 menting the tone, by placing the vibrating rods over common 

 small phials, which gave a tone by blowing on them. 



Instead of the organ-pipes, Chladni used common wide-bel- 

 lied medicine glasses of one or two ounce capacity, and tunes 

 them, when, by blowing on them, they gave a deeper tone 

 than the pitchpipe, by pouring water into them, (so as to 

 lessen the air column in the glass exactly in the same manner 

 as a closed organ-pipe is shortened,) so as to bring them into 

 accord with the pitchpipe. As soon as this happens, the sound 

 of the pitchpipe held over the glass becomes stronger. And 

 if the pitchpipe, when struck, is now turned before the mouth 

 of the small tuned ounce glass in a circle, (in the same manner 

 as formerly before the ear,) the tone becomes four times 

 stronger, and four times again vanishes, when it is, as formerly, 

 placed in the diagonal position. 





