chap, xx.] PRODUCTION OF WAVES. 219 



less extensible the tube the faster will the wave travel, 

 while a slow rate, a retarded wave, means great exten- 

 sibility. The wave increases also with rapidity of the 

 impulses, and diminishes with increased density of fluid. 

 The Iiesgiit of the wave depends upon the ex- 

 tensibility of the walls of the tube. The more easily 

 distended the tubes are the higher will be the wave, but 

 the less will be its length. For if an additional quan- 

 tity of fluid be projected into a tube which readily 

 distends, a small portion of the tube will increase 

 its diameter sufficiently to contain the added quantity. 

 If, on the other hand, the tube is distended with 

 difficulty it will yield little to the increased pres- 

 sure, and, in consequence, a greater extent of wall 

 must yield in order to accommodate the added quan- 

 tity of fluid. Thus, the height of the wave will be 

 little, but its length will be considerable. Now it 

 is easily understood how one and the same tube may 

 present, at one moment, the features of a readily dis- 

 tensible tube with high short waves, and, at another 

 moment, the features of a tube distended with 

 difficulty showing low but long waves. Suppose a 

 moderately distensible tube which has a fluid flowing 

 through it under so little pressure that the tube is 

 hardly distended at all, the projection into the tube of 

 additional quantities of fluid will distend it consider- 

 ably at every projection, and the characters of a high 

 short wave will be produced. Let the same tube be 

 traversed by a fluid at great pressure, which, acting 

 on the elastic walls, distends them to their utmost 

 capacity. Under these circumstances the tubes are 

 nearly in the condition of a rigid tube, the projec- 

 tion of new quantities of fluid into it are capable of 

 dilating it further only to a very small amount, and 

 the characters of a low long wave are produced. The 

 application of these phenomena to the production of 

 the pulse will appear immediately. 



