MUSICAL SOUNDS FROM VIBRATION OF AIR. 185 



where the particles of the air have the greatest 

 motion, will be violently agitated, while at points 

 nearer the ends A and B it will be less and less 

 affected. 



Let us now suppose two pipes, AB, BC, to be 

 joined together as in Fig. 42, and to be separated 

 by a fixed partition at B ; and let a spiral spring 

 be fixed in each. Let the spring A B be now 

 pushed to the end A, while the spring BC is 

 pushed to C, as in No. 1, and back again, as in 

 Fig. 42. 



c 



N'2 



No. 2,^ but always in opposite directions ; then it 

 is obvious that the partition B is in No. 1 drawn 

 in opposite directions towards A and towards C, 

 and always with forces equal to each other : that 

 is, when B is drawn slightly towards A, which it 

 is at the beginning of the motion, it is also drawn 

 slightly towards C; and when it is drawn forcibly 

 towards A, as it is at the end of the motion of 

 the spring, it is also drawn forcibly towards C. 

 If the partition B, therefore, is moveable, it will 

 still remain fixed during the opposite excursions 

 of the spiral springs; nay, if we remove the 

 partition, and hook the end of one spiral spring 

 to the end of the other, the node or point of 

 junction will remain stationary during the move- 

 ments of the springs, because at every instant 

 that point is drawn by equal and opposite forces, 



