THE REVOLVING DRUM 21 



drum (w, Fig. 7), and (2) by putting in a high or low 

 gear. The direction of revolution of the drum is reversed 

 by twisting the belt connecting the pulleys into a figure 

 of 8. 



Make yourself acquainted with the method of use of 

 the three following drums : 



a. Fig. 7. In this cogs at the end of the axle of the 

 pulleys w can be geared into the cogs of a small or a 

 large wheel on the spindle of the drum. In Fig. 7 the 

 high gear is engaged. To engage the low gear, pull back 

 the pulleys w, raise them so that the cogs on the axle 

 engage with wheel c, and clamp. Turn the whole drum 

 till the pulleys w are in line with the pulleys on the shaft 

 driven by the motor. 



When the gears are engaged the drum must not be 

 turned by hand either backwards or forwards. If it is 

 required to revolve the drum by hand, take off the belt 

 and turn round the pulleys w, or take off the belt, dis- 

 engage the gearing and turn the drum itself. 



The key (k, Fig. 7) is called a knock-down key. It is 

 used as an in-circuit key in the battery current, so that 

 when the drum revolves, the arm (a) knocks down the 

 vertical rod (b) and breaks the current. 



b. Lucas drum. In this 1 the gearing is inside the 

 case at the base of the drum. The slow gear is engaged 

 when the steel spring (Sp, Fig. 8) is in the upper groove 

 G and the high gear when the spring is in the lower 

 groove G' '. The spring can easily be moved from one to 

 the other by the fingers. It must not be moved above 

 groove G or below groove G'. The knock-down key is 



1 Made by the Cambridge Scientific Instrument Co. 



