12 UNIVERSITY OF MISSOURI STUDIES 



Let US now imagine a third case. Suppose a partition 

 to divide the tube lengthwise into two divisions, leaving, 

 however, a small opening of communica- 

 The effect of a '•'°" between the divisions at x. Suppose 

 flexible, but inelas- further this partition to be neither per- 

 tic partition with- fectly rigid like a wall of hard bone nor 

 m the tube as readily yielding and in turn contract- 



ing as a thin rubber membrane, but to be 

 of the physical nature of a soft leather strap somewhat 

 loosely stretched out between the opposite sides of the 

 tube to which it is assumed to be well attached. To have 

 something definite in mind, let the reader think, for compar- 

 ison of its function, of a leather- seated chair. If you press 

 from below, the seat yields and bulges upwards; but 

 soon it stops in spite of your effort. If now you sit down 

 on the chair, the seat bulges downwards; but again, it 

 soon stops — how could it otherwise be used for the support 

 of your weight? But what is particularly important to note 

 here, is the fact that the leather seat, after it has bulged 

 either way, may continue to remain thus until some ex- 

 ternal force acts upon it again from the other side. Now 

 let us consider the movements which Avould occur in the 

 fluid of a tube, divided into two divisions by a partition 

 of the nature just described. If the partition could yield 

 indefinitely, the case would obviously be practically the same 

 as the first one we studied — without any partition. That 

 is, the fluid would move near the two windows and the part 

 of the partition suspended between moving masses of fluid 

 would move with the fluid. Farther on where the fluid re- 

 mains motionless the partition would remain motionless too. 

 But we made the assumption that the partition, like the seat 

 of a leather-seated chair, can move only within certain 

 narrow limits up and down. Now, the result of this condi- 

 tion will be this. When the stirrup begins moving inwards. 



