1 86 PHYSIOLOGICAL PHYSICS. '[Chap. xvm. 



acting on the yielding caoutchouc membrane raises it 

 upwards ; and the movement is indicated by an 

 upward stroke of the lever. Thus a movement almost 

 imperceptible in the membrane itself will be rendered 

 quite visible by the lever. Again, if the membrane of 

 one tambour be raised or pulled upwards the air 

 within it will be rarefied. The rarefaction, acting 

 through the indiarubber tubing, will cause the 

 membrane of the second tambour to be depressed, 

 and this movement the lever will indicate by a down- 

 ward stroke. Thus with a system of two tambours a 

 downward movement of the membrane of one causes 

 an upward movement of the lever of the other, and 

 vice versa. If, however, it is desired to give the same 

 direction to both, it is only necessary to turn one 

 tambour upside down. Thus, not only may move- 

 ments be transmitted from a distance, but the move- 

 ment may be recorded in any direction at will, for the 

 tambour which writes the movement may be placed 

 so as to write on a horizontal cylinder, or may be 

 turned so as to write on a vertical cylinder. Thus a 

 horizontal may be converted into a vertical movement, 

 or vice versa, and otherwise. 



The tambour which receives the movement is 

 called the receiving or transmitting tambour, and that 

 which writes as the registering or recording tambour. 

 The registering tambour will retain in all cases the 

 form described, being supported on a horizontal or 

 vertical arm, as may be wished, and its lever point 

 brought against the blackened moving surface. The 

 tambour, however, which receives the impulses to be 

 transmitted, is modified to suit the circumstances of 

 each case. Thus, Marey has adapted the instrument 

 for the purpose of obtaining a note of the contacts of 

 each foot with the ground in running. A shoe has in 

 its sole one tambour in the form of an air-chamber, 

 the air of which is compressed by the pressure of the 



