PHYSIOLOGIC APPARATUS 



769 



The Recording Surface. The surface which receives and records the 

 movements of a pen or lever is usually that of a cylinder which is covered 

 with glazed paper and coated with a thin layer of soot, obtained by passing 

 the cylinder through the flame of a gas burner. The axis of the cylinder is 

 supported by a metal framework. If the writing point of the lever be placed 

 against the cylinder and a movement be imparted to it, a portion of the soot is 

 rubbed off, leaving a white line behind. If the cylinder be stationary, the 

 rise and fall of the lever are recorded as a vertical line. Such a record shows 

 only the extent of a movement. 

 If the cylinder is traveling, how- 

 ever, at a uniform rate, the rise and 

 fall of the lever are jecorded in the 

 form of a curve the width of the 

 two arms of which will depend 

 partly on the rapidity of the move- 

 ment of the lever and partly on the 

 rate of movement of the cylinder. 

 The cylinder movement is initiated 

 and maintained by clock-work or 

 by the transmission of power by 

 belting to a system of pulleys in 

 connection with its axis. As the 

 tracing is wave-like in form, the 

 cylinder is frequently spoken of as 

 a kymograph or wave recorder 

 (Fig. 344). 



From the record thus obtained 

 it is possible to determine not only 

 the extent but also the duration, the 

 form, and the rate of recurrence of 

 any given movement. 



The Extent of a Movement. As 

 the lever not only takes up and re- 

 produces a movement, but at the 



.r ., .' . , . , FIG. 344. KYMOGRAPH. (Boruttau s. Pet- 



same time magnifies it, it is essential zo l ( j j Leipzig.) 



that the degree of magnification be 



known, in order to determine the actual extent of the movement. The 

 magnification of the lever is readily determined by dividing the distance 

 between the axis of the lever and its writing point by the distance between 

 the axis and the point of attachment of the structure, and then dividing 

 the height of the tracing by this quotient. The final quotient represents 

 the extent of the movement. 



The Time Relations of a Movement. When recorded in the form of a 

 curve, the duration of the entire movement, or of any one portion of it, can 

 be determined by means of a time marking or chronographic apparatus, con- 

 sisting of (i) a small signal magnet provided with a movable armature, to 

 which is attached a writing style; (2) an automatic interrupter; and (3) an 

 electric cell. 



The Signal Magnet. The magnet (Fig. 345) is actuated by the electric 

 current made and broken at regular and known intervals by an automatically 



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