232 



OPTICAL PROJECTION 



way to circumference. These two discs are arranged one on 

 each side of the upper part a a of the slide B, and are caused 

 to revolve in opposite directions by a crown wheel working 



between them ; 

 this wheel is 

 shown at s, with 

 the rod r 1 r 1 r 1 " 

 connecting it by 

 the winch /with 

 the handle K. 

 The wheel V 

 simply gears into 

 a', and has com- 

 plete waved 

 radial lines: all 

 these lines are 

 cut in black 

 ground and 

 coloured red. 

 The circular mo- 

 tion of these 

 lines over the 

 painted dia- 

 grams, as will be 

 seen on reference 

 to the enlarged 

 diagram in fig. 

 119, gives a very 

 graphic idea of 

 the circulation as 

 there depicted. 



. 119 126. Physio- 



logical Move- 

 ments. The simplest optical demonstration of any vital 

 phenomenon is that of the pulse by a small reflecting mirror 



