70 SECTION PHYSICS. 



such a length as to resound to the successive notes of the diatonic 

 scale, when a burning gas-jet is raised to the proper point of the 

 tube by pressing down the keys. This instrument is from the Wheat- 

 stone Collection of Physical Apparatus at King's College. A 

 photograph of a similar instrument is exhibited by Professor Oppcl 

 of Frankfort. 



Wheatstone investigated experimentally the laws of vibration in 

 conical tubes, and showed the agreement between the calculations of 

 Bernouilli and experiment. For the first mode of vibration, i.e., for the 

 lowest note of a conical pipe, all the air in the pipe moves backwards 

 and forwards in the same direction at the same time. The particles 

 alternately approach to and recede from the apex of the cone. In the 

 second mode of vibration there is a ventral section in the middle of the 

 pipe, and the pipe is divided by it into two parts of equal length. In 

 the third mode of vibration there are three equal lengths separated by 

 two ventral sections. 



Taking conical tubes, the different notes which may be produced 

 from them correspond precisely to those which maybe produced from 

 open cylindrical pipes of the same length. Taking this conical tube, 

 two feet long, the resonance corresponds to a middle C tuning fork, 

 and if from any cone I take a part of the same length and open at 

 both ends, I shall get the same note, so that with a conical pipe, either 

 closed at the apex or open at both ends, we get the same note as from 

 a cylindrical open pipe of the same length. The harmonics produced 

 in the conical pipe are the same as those in the open cylindrical pipe, 

 which are of course different f;om those produced by closed cylindrical 

 pipes ; the difference being seen in two musical instruments, the clarionet 

 and the oboe. The oboe being conical the harmonics are those of an 

 open cylindrical pipe. Cutting up the cone into equal lengths, we get 

 the same note from each, so that if these short pipes, which were Sir 

 Charles Wheatstone's, are sounded, the same musical note will be pro- 

 duced from each of them, but in each of these open pipes there is a 

 node which is not at the centre of the pipe. In a cylindrical pipe the 

 column of air will be divided equally into two vibrating parts at a node 

 in the centre, but in the conical tube the node is not in the centre but 

 will be nearer to the smaller end of the tube. As the pipe tapers more 

 moie, the distance of the node from the centre of it will be more 



