PROPAGATION OF PULSE-WAVES IN ELASTIC TUBES. 



153 



according to Bonders, 11-14 metres (34 - 43 feet). (2) According to E. H. Weber 

 increased internal tension causes only an inconsiderable decrease ; Rive found a 

 great decrease ; Donders found no obvious difference ; while Marey found an increased 

 velocity. (3) Donders found the velocity to be the same in tubes, 2 mm. in dia- 

 meter, as in wider tubes, but Marey believes that the velocity varies when the 

 diameter of the tube changes. (4) The velocity is less the smaller the elastic 

 coefficient. (5) The velocity increases with increased thickness of the wall, while 

 it diminishes when the specific gravity of the fluid increases. 



Moens has recently formulated the following laws as to the velocity of propaga- 

 tion of waves inelastic tubes: (1) It is inversely proportional to the square root 

 of the specific gravity of the fluid. (2) It is as the square root of the thickness 

 of the wall, the lateral pressure being the same. (3) It is inversely as the square 

 root of the diameter of the tube, the lateral pressure being the same. (4) It is 

 as the square root of the elastic coefficient of the wall of the tube, the lateral 

 pressure being the same (Valentin). 



Experiments With Caoutchouc Tubes. For this purpose Landois employs 

 the following apparatus (Fig. 67): A large tuning-fork, A (35 cmtr. long), carries 

 on one of its arms a glass-plate, P (25 cmtr. long, and 5 cmtr. broad), while the other 

 arm is weighted, G. The tuning-fork is fixed by an iron holder, T, to a movable 

 piece of wood which can be pushed along with the hand in a groove on a support 

 H, H. When the glass-plate is smoked, the curved needle of the angiograph 

 writes its movements upon it. The fork, when it vibrates, makes little teeth in 

 the curve, and the value of each vibration is estimated beforehand. Every com- 

 plete vibration in this instrument is equal to 0'01613 sec. 



Velocity of the Waves in Elastic Tubes filled with Water or Mercury. 



Take a soft extensible elastic tube, A, 8 '80 metres long, 1 mm. thick, and 



Fig. 67. 



Instrument for measuring the velocity of the pulse-wave in an elastic tube con- 

 taining water or mercury A, tuning-fork ; B, ampulla ; A, elastic tube ; P, 

 glass-plate smoked; Q, manometer; x, pad of lever of angiograph; writing- 

 style, D. 



