STEAM AND GASOLINE ENGINES 



197 



it transmits its rotation 

 to a secondary shaft on 

 which are cogwheels of 

 various sizes (Fig. 80). 

 The operation of the 

 clutch may be illustrated 

 thus: Set the eraser of 

 your pencil down on a 

 card or sheet of paper 

 on a smooth table, then 

 give the pencil a rotary 

 motion between your 

 fingers. If the rubber is 

 at the same time pressed 

 on to the card, the latter 

 will also turn around. 

 One face of the solid fly- 

 wheel has pressed against 

 it a disk on the end of 

 the secondary shaft, and 

 so this shaft turns with 

 the wheel. The pressure 

 is maintained by a spring 

 except when the clutch 

 pedal is in. In most 

 machines now, the clutch 

 is of a multiple-disk 

 variety in which several 

 disks on the secondary 

 shaft engage correspond- 

 ing projecting plates on 

 the flywheel. 



By means of the 

 gear-shift lever, cog- 

 wheels of several sizes 



