IMPROVEMENTS IN CLOCK-ESCAFEMENTS. 



421 



part, or that which is given in about the first 60° and the last 60° of the 180° through 

 which the scape-disc moves at every beat. This is done by using a scape-wheel with three 

 pins or teeth instead of one; and the wheel and pallets then assume this form, which 



Three-legged dead Escapement : full-size for a Turret-clock ; (the pallet arbor to be 12 inches above the 



scape- wheel.) 



pendulum 



left of zero 



pendulum 



pretty obviously suggests the name of the three-legged dead escapement. The impulse is 

 given on the vertical faces of the pallets, as the tooth in action passes through its high- 

 est or lowest arc of 60°, with scarcely any friction. And the consequence of this great 

 saving of friction in the impulse is a diminution of the pressure and friction on the dead 

 pallets far beyond what I had expected, although I had already learnt from MacdowalFs 

 escapement that there was more force wasted in friction in the common dead escapement 

 than anybody appears to have been aware of before. The pendulum of the Westminster 

 clock, in order to get its length adjusted, had been previously set going with a common 

 church-clock movement and pinwheel escapement, and then it required a weight of 80 lbs. 

 to make it swing the usual arc; but when this three-legged escapement was put to it, 

 they were obliged to take off all the weight except 15 lbs. So that at least four-fifths of 

 the proper duty of the scape-wheel is wasted in first producing and then overcoming the 

 friction of the common dead escapement. I say 'at least 1 four-fifths, because even 

 in this new escapement there is some dead friction, and moreover, I found that it had 

 been made with an unnecessary amount of clearance, so that nearly a quarter of the impulse 

 was lost in the drop of the teeth on to the pallets. The dead friction however is so small, 



54—2 



