of the Royal Society of Edinburgh. 347 



friction is reduced as much as possible, by forming the scape- 

 wheel of steel, and the pallets of jewels ; but oil is still neces- 

 sary, and however pure, it must be liable both to chemical 

 change, and to a gradual admixture with dust; its effect there- 

 fore on the rubbing parts must vary, and the impulse given to 

 the pendulum must vary with it. 



The escapement, which I shall now proceed to describe, is 

 the invention of Mr WHITELAW, a very ingenious artist in this 

 city, who has been employed to make the clock. His escape- 

 ment possesses the advantage of not requiring oil in any part of 

 its mechanism, and therefore is free from one great cause of ir- 

 regularity. 



In the drawings, at Figs. 2. 3. and 4., A is a scape-wheel, 

 which need not vary much from the usual form ; it acts alter- 

 nately on the pallets D and E. These pallets are not attached to 

 an intermediate axis, as in the former case, but are fixed to the 

 pendulum itself (by which arrangement some sources of irregu- 

 larity are suppressed). C C are the branches which carry the 

 pallets ; and B is the knife-edge on which the pendulum oscil- 

 lates. 



The pallets D and E, instead of being inclined planes along 

 which the teeth of the scape-wheel would be required to slide 

 while giving impulse to the pendulum, are portions of the sur- 

 faces of cylinders which revolve (or rather oscillate) on delicate 

 pivots in ruby holes. When a tooth of the scape-wheel drops 

 on one of these cylinders during the motion of the pendulum, 

 the cylinder is turned partly round by the continued action of 

 the tooth, until the pendulum has swung so far that the tooth 

 escapes past the cylinder, having descended through a space equal 

 to half of its diameter : at the moment of its escape, a tooth on 

 the opposite side of the wheel is arrested by the other pallet, 

 and a similar escape takes place with that tooth on the returning 

 swing of the pendulum. 



VOL. XI. PART II. X X 



