558 
SECOND REPORT - 1832 . 
3. ACOUSTICS. 
Mr. Wheatstone exhibited an experimental proof, which he 
had devised, of the following result of Bernouilli's theory of 
wind instruments :—that in the fundamental sound of a tube, 
open at both ends , the portions of air on opposite sides of the 
centre of the tube move in contrary directions to each other. 
It consisted of a leaden tube, about an inch in diameter and 
thirteen inches long, bent nearly into a circle, so that its two 
ends were near, and opposite to, each other. Between these 
ends was held a vibrating part of a square plate of glass, put 
into vibration either with a violin-bow or a hammer, so as to 
produce its lowest sound, corresponding with Chladni’s first 
figure. By this arrangement, the plate, advancing in its vibra¬ 
tion towards one end of the tube, and receding at the same in¬ 
stant from the other, the effects neutralize each other, and no 
resonance or augmentation of the original sound takes place. 
In the middle of the tube was a joint, which allowed each half 
to move independently round the axis of the tube ; by this 
means the two ends were capable of being brought to the op¬ 
posite sides of portions of the plate vibrating at the same mo¬ 
ment on contrary sides of the neutral plane; in this case, the 
impulses were made at the same instant towards both ends of 
the tube, and the augmentation of sound was very considerable. 
It is obvious that these effects would be reversed were Ber- 
nouilli’s theory wrong. 
Mr. Wheatstone gave an abstract of his Researches on the 
acoustical figures of vibrating surfaces. In the first part of 
this inquiry the author confined himself to the consideration of 
the figures of square surfaces only, and after stating the general 
results of Chladni's experiments, proceeded to show that all 
the figures, however complicated in appearance, were the re¬ 
sultants of simpler modes of vibration, exactly similar to, and 
superposed upon, each other. The nodal lines of the elemen¬ 
tary modes of vibration he showed might be either parallel to 
a side, to a diagonal, or to any other intermediate direction: in 
the two first cases, the plate admits but of two coexisting similar 
modes of vibration, but in all other cases of four. He described 
various processes for combining the component figures and 
ascertaining their resultants, and exhibited an extensive general 
table of perfect resultant figures, calculated according to the 
rules he had discovered. He then proceeded to show the ap¬ 
plication of these laws to the figures of other rectangular plates, 
