394 POPULAR LECTURES AND ADDRESSES. 



screws upwards, increasing- the force of the springs. 

 Once every scmipcriod of the pendulum it is held 

 back by either pallet, and the nut collar screws down 

 as much as it rose during the preceding interval of 

 freedom when the action is regular ; and the 

 central or main escapement-shaft turns in the 

 same period as the tooth, being the period of the 

 pendulum. If, through increase or diminution of 

 the driving-power, or diminution or increase of the 

 coefficient of friction between the governing masses 

 and the ring on which they press, the shaft tends 

 to turn faster or slower, the nut collar works its 

 way clown or up the screw, until the governor is 

 again regulated, and gives the same speed in the 

 altered circumstances. It is easy to arrange that 

 a large amount of regulating power shall be implied 

 in a single turn of the nut collar relatively to the 

 central shaft, and yet that the periodic application 

 and removal of about - 1 ,,- of this amount in the 

 half period of the pendulum shall cause but a very 

 small periodic variation in the speed. The latter 

 important condition is secured by the great moment 

 of inertia of the governing masses themselves round 

 the main shaft. 



