Royal Institution of Great Britain. 463 



March "16.— Mr. Wheatstone on the Vibrations of Columns of Air 

 in cylindrical and conical Tubes. 



After enumerating the various modes by which columns of air may- 

 be put into sonorous vibration, and which constitute so many classes 

 of wind instruments of music, Mr. Wheatstone proceeded to detail 

 the principal results of Bernouilli's Theoretical Investigations. When 

 a column of air in a cylindrical tube, open at both its ends, produces 

 the lowest sound it is capable of rendering, acccrding to this theory, 

 the motions of the particles of air are made in opposite directions, 

 alternately to and from the central point or node, where the varia- 

 tions of density are greatest. Mr. Wheatstone gave the following 

 new and decisive experimental proof of this theoretical deduction. 

 He took a tube bent nearly to a circle so that its ends were opposite 

 to each other, with a small space between them ; he then took a glass 

 plate, capable of making the same number of vibrations as the air 

 contained within the tube, and causing it to sound by drawing a 

 violin bow across it, placed it at equal distances between the two 

 orifices, so that the impulses of the vibrating surface were made, at 

 the same in-tant of time, towards one, mAfiom the other end of the 

 tube : as might be expected from the theory, these effects neutra- 

 lizing each other, no resonance took place, and the air in the tube 

 remained at rest. But when (the two halves of the tube moving 

 round each other by means of a joint,) the orifices were brought op- 

 posite to different vibrating parts of the plate, so that the impulses 

 were made at the same instant towards or from both the orifices, 

 the column of air powerfully resounded. 



He then proceeded to show, tb.at when a column of air sounded 

 any other than its fundamental note, it did so in consequence of a 

 division of the column into parts of equal length separately vibrating, 

 in the same manner as the harmonic sounds of a string liave been 

 explained: that the air mav vibrate when divided into any number 

 of aliquot parts, and the corresponding sounds are as the series of 

 natural numbers, 1, 2, 3, 4, 5, 6, &c. : that, at the limits of each 

 vibratin"- part, a communication may be made with the atmosphere, 

 by an arjcrture, or even by entirely separating the tube, without any 

 injury to the sound: that, in each mode of division m which there 

 is a node in the centre, (i. e. in each alternate node,) a solid partition 

 mav be placed at the centre of the tube, dividing it into two equai 

 par'ts, each giving the same sound as the entire tube when the par- 

 iition was removed: and that, consequently, a tube stopped at one 

 end gives a series of sounds corresponding to the progression 1, o, 

 5, 7, &c. of a pipe double its length and open at both ends. 



After verifying these established results, he proceeded to show 

 the error of the prevailing opinion, stated by Chladni and others, 

 " that the end at whicl, a tube is excited into vibration, must always 

 be considered as an open end, eve,, if it be placed immediately to 

 the mouth, as in the horn and trumpet." He showed that a cylin- 

 drical tube gave the same fund.-.mental sound and the same series of 

 harmonics, when it was excited as a l.orn, or with a reed, at one end, 



the 



