382 



NOTES PRODUCED BY MEANS OF TUBES. 



Fig. 230 shows the relative position of the indiarubber tube and 

 glass tube (the fingers which hold the rubber tube are left out). 

 To save the trouble of pressing the end every time with the 

 fingers, thin wire softened by annealing may be wrapped round the 

 tube and then pressed together into the required shape. The end 

 of the tube is kept in shape by the wire. 



The flute is a tube open at both ends, 'one aperture 

 however, being not quite at the end, but near it and at 

 the side. A current of air is directed by the 

 lips over this lateral opening. The so-called 

 4 flue ' - pipes of an organ, and common 

 whistles, are tubes which have also a lateral 

 aperture at one end, and are either open or 

 closed at the other end ; a current of air is 

 directed through a narrow slit, and strikes the 

 opposite sharp edge of the aperture or 'mouth r 

 of the instrument. Fig. 231 shows the con- 

 struction of a wooden organ pipe, which differs 

 very little from that of a common whistle. The 

 figure shows a section through the length of 

 the tube, which is square ; organ-pipes of meta 

 are round, and flattened only near the mouth. 

 The rate at which the longitudinal vibra- 

 tions of the air in tubes take place, and 

 hence the pitch of the notes produced, de- 

 pends, like the similar vibrations of rods, 

 principally upon the length of the vibrating 

 mass : the number of vibrations is in the 

 inverse ratio of the length. Four tubes 

 which are to produce a perfect major chord, 

 j n wn i c h the vibrations are in the ratios 

 * 2, must have their lengths in the ratios 1: -J: 

 for example, they may be respectively 30, 24, 20, 



al?' 2 fo' 

 real size}. 



1: 2 



