234 OPTICAL PROJECTION 



easily and simply done in ways too obvious to need descrip- 

 tion ; or films of smoked mica can be bent round the cylinders, 

 and afterwards unrolled and mounted between glass plates. 

 To take the case before us : when the break in the curve has 

 once been shown in actual motion on the screen by the pulse- 

 mirror, and its method of production explained, it will be 

 found that the meaning of the curve in any tracings subse- 

 quently projected will be instantly realised in a degree very 

 desirable. 



This will be still more the case if the process of tracing 

 be itself projected, which can generally be done, by the ap- 



FIG. 121. Double Recording Apparatus 



paratus devised by Marey. The usual means of transmitting 

 vital movements to the recording style or point need not be 

 described in detail, as it is well known that the two principal 

 methods are the electric current, or Marey 's tambour. By 

 arranging an apparatus as in fig. 121, where the screw d 

 adjusts upon the main pillar an electric receiving apparatus m 

 in electrical connection at c, while the screw e adjusts another 

 recording style actuated at g by the registering tambour n, 

 whose membrane on the top is actuated by the varying pneu- 

 matic pressure conveyed into the receiving tambour by a tube 

 at r, the motion transmitted electrically and pneumatically 



