392 POPULAR LECTURES AND ADDRESSES. 



collar projects inwards to the furrow of the screw, 

 so that, if the collar is turned relatively to the 

 shaft, it will be carried up or down, as the nut of 

 a screw, but with less friction than an ordinary 

 nut. The main escapement-shaft just described is 

 mounted vertically. Below the screw and long 

 nut-collar, the escapement-shaft is surrounded 

 by a tube which, by wheel-work, is carried 

 round about five per cent, faster than the central 

 shaft. This outer shaft, by means of friction 

 produced by the pressure of proper springs, carries 

 the nut collar round along with it, except when 

 the escapement-tooth is stopped by cither of the 

 pallets attached to the pendulum. A stiff cross 

 piece (like the head of a T), projecting each way 

 from the top of the tubular shaft, carries, hanging 

 down from it, the governing masses of a centrifugal 

 friction governor. These masses arc drawn towards 

 the axis by springs, the inner ends of which arc acted 

 on by the nut-collar, so that the lower or the higher 

 the latter is in its range, the springs pull the masses 

 inwards with less or with more force. A fixed 

 metal ring coaxial with the main shaft holds the 

 governing masses in, when their centrifugal forces 



