376 THE VIBRATIONS OF GASEOUS BODIES. 



represented at J., and the air in the tube has in this casi 

 clearly the same density as the external air. When the 

 air in the tube is made to vibrate, all particles, except 

 the one in the centre, move at the same instant from 

 their position of rest; the particles on the left of thi 

 centre move towards the left, those on the right movt 

 towards the right, fig. 226 B. The nearer a particlt 

 is to the centre, the shorter is the space through whicl 

 it passes ; the largest spaces are described by the par- 

 ticles at either extremity of the tube. The centre of thi 

 tube is a node, while each end is the middle of a ventra 

 segment. The density of the air in the tube is at tin 

 same time diminished since the particles of air, repre 

 sented by the lines, recede from one another ; but th< 

 rarefaction is not equal at the different points: at tk' 

 ventral segments, where the particles are farthest fron 

 their position of equilibrium, the rarefaction is least, bu 

 it is greatest at the nodes. This is also easily seen fron 

 the figure. When the particles of air have reached thei 

 greatest distance from the position of equilibrium, the; 

 return, reach again the position of equilibrium, and pas 

 beyond it to the opposite side ; that is, the particles c 

 air in that portion of the tube which is on the left mov 

 to the right, those in the right move to the left and 

 condensation of air takes place in the whole of the tuk 

 The condensation is likewise greatest at the nodes an- 

 least at the ventral segments, as seen in fig. 226 C 

 From the state of condensation the particles of air retur 

 again to the position of equilibrium, and the whol 

 movement is repeated in the same successive order ; 

 described. 



