218 PHYSIOLOGICAL PHYSICS. [Chap. xx. 



tambour, causes oscillations of the air inside. These 

 oscillations are communicated through a tube to a 

 registering tambour, whose style presses on the surface 

 of a revolving cylinder. The box tambours are placed 

 at intervals along the elastic tube, each communicating 

 with a registering one. The styles of all the registering 

 tambours are arranged on the same recording surface, 

 one after the other in their proper order. Thus the 

 progression of the wave and other occurrences in the 

 fluid are registered on the same surface, and may be 

 studied at leisure. 



It has been seen that it is intermittence of action 

 that produces the wave movement. Marey has shown 

 that the EXTENT OF THE WAVE depends on the sudden- 

 ness of the disturbance of equilibrium, and, when it is 

 due to the propulsion into the tube of an additional 

 quantity of fluid, it is proportional to the quantity. 

 Greatest at the moment of its production, it gradually 

 diminishes up to the end of the tube, if it be not 

 closed. A brief energetic impulse is capable of pro- 

 ducing, not only the primary wave, but a series of 

 SECONDARY WAVES. This is due to the fact that the 

 molecules of the liquid have been displaced above the 

 level of their normal position, as they took part in the 

 formation of the crest of the wave, and have then fallen 

 below their normal level in forming the hollow of the 

 wave. So that when, with the completion of the wave 

 movement, so far as each molecule is concerned, the 

 molecules are restored to their former position or level, 

 the force they have acquired compels them to pass 

 again beyond the normal, first in one direction and 

 then in the other. So they oscillate backwards and 

 forwards, producing secondary waves, until the ac- 

 quired energy is dissipated and they come to rest in 

 the usual position. 



The speed of propagation of the wave is pro- 

 portional to the elastic force of the tube. Thus, the 



