PHYSIOLOGICAL DEMONSTRATION 235 



may be traced upon the same blackened plate by the styles a 

 and b ; and if the plate and styles be adjusted in front of the 

 condensers, and focussed on the screen, the tracings will 

 appear as they are made. In some cases it may be well to 

 attach fine wires carrying small black discs to the ends of a 

 and 6, and to exhibit the motion of these discs upon the 

 screen, before the clockwork tracing is made. 



By employing the delicately-adjustable tambour devised 

 by Marey for the purpose, as the transmitting instrument in 



FIG. 122. Projection of Heart Movement 



a pneumatic system, or two systems, the movement of the 

 heart may be shown from the outside of the chest upon the 

 screen, or simultaneously with a pulse -tracing. All that is 

 really necessary is to adjust the clock-work movement and 

 the traverse of the tracing point, to the size of the field 

 covered by the condensers of the lantern. As regards the 

 projection itself, it is only needful to secure an evenly illu- 

 minated disc, in the manner described on p. 115, for the focal 

 plane which is to be occupied by the blackened glass. This 



