NOTES PRODUCED BY MEANS OF TUBES. 383- 



and 15 cm long. We have seen that a tube closed at one 

 end gives out the same note as that produced by a tube 

 of double the length and open at both ends ; the number 

 of vibrations in the former is therefore one half of the 

 number of vibrations of a tube of the same length, but 

 open at both ends. In other words, the note produced 

 by a tube closed at one end is an octave below the note 

 produced by a tube open at both ends, if both tubes 

 have the same length. 



If the student cannot procure proper instruments for these experi- 

 ments, tubes made of stout paper or very thin cardboard may be used. 

 They do not emit musical notes, but allow of a sufficiently distinct 

 determination of the pitch of their sound for confirming the law 

 stated above, on the relation between the length of the tube and the 

 number of vibrations. 



Strips of paper or cardboard, of the length stated (15 to 30 cm ) 

 and from 7 to 10 cm broad, are rolled round a cylindrical rod or stout 

 glass tube, so as to bend them into cylindrical shape, and the long 

 edges are then glued together. If such a tube, after being dried, is 

 allowed to fall horizontally upon a table, it emits a sound which by 

 itself is not very distinct ; but if the four tubes are dropped in rapid 

 succession, the gradation in the pitch of the four notes which con- 

 stitute the chord will be distinctly heard. Let another tube be 

 made out of a strip I r 6 cm long and 10 cm broad, and one end be 

 closed by a circular piece of cork, l cm thick, which is fixed with glue- 

 into the end, leaving inside the tube a clear length of 15 cm . If the 

 tube be held inclined, the closed end resting on the table, and 

 allowed to fall, the sound will be found to have the same pitch as 

 that of the tube 30 cra long which is open at both ends. Instead of 

 letting the tubes fall, they may also be placed upon some soft 

 support (a piece of cloth), and sounded by knocking them gently 

 with a pencil. If a series of eight tubes be made, of the respective 

 lengths, 36, 32, 28'8, 27, 24, 21-6, 19'2, and 18 cm , they will sound 

 the whole scale in B flat major, 



C 1) Et?F G A B 



6'b c" d" e"b f f cj" a" V") 



and it will be possible to play whole airs upon the tubes. 



