80 GENERAL PROPERTIES OF LIVING TISSUES 



a bearing without " sidelash " and with little friction. 

 As the sleeve with the drum rests upon the friction 

 plate by gravity alone, it is easy to turn the drum by 

 hand either forward or back, even while the clock- 

 work is in action. At the top of the sleeve is a screw 

 ending in a point which, when the screw is down, 

 bears upon the end of the steel shaft and lifts the 

 sleeve, and with it the drum, until the sleeve no 

 longer bears upon the friction plate. The drum may 

 then be " spun " by hand about the steel shaft. The 

 impulse given by the hand will cause the drum to 

 revolve for about one minute. The speed during any 

 one revolution is practically uniform. 



The clockwork consists of a stout spring about 

 6 metres in length, driving a chain of gears. The 

 speed is mainly determined by a fan slipped upon an 

 extension of the last pinion shaft in the chain. Four 

 fans of different sizes are provided. 



The speed is regulated by a governor on the shaft 

 that carries the fan. When the milled head shown to 

 the right of the steel shaft in Fig. 19 is up, the gear 

 on the extreme right of the chain no longer engages 

 with the gear driven by the spring, but runs " idle," 

 while the gear attached to the friction plate engages 

 with the lower of the two gears at the left ; the pinion 

 of this lower left-hand gear engages with the spring 

 gear. Fast speeds are then obtained. 



When the milled head is down, the gear attached 

 to the friction plate falls below the left-hand gear, 

 while the right-hand gear engages with the spring 



