^^0 TIMEKEEPERS. 



•ut an equal quantity of the two mean time screws hh, ancf 

 should it lose, decrease the diameter, by screwing in an equal 

 quantity of the same screws. This adjustment does not 

 affect for that heat and cold, because these screws are uncon- 

 nectfd with the expansion pieces, nor will they affect the 

 positions, if they are both turned the same quantity, and the 

 taps of the same thread. 



Of the Escapement. 

 DcscripHon Fig. 5, represents the escapement wheel, [supposed to be 



tlu- detached ^'o'^f^ to motion by the train] the teeth of which are of 

 «scjpeiTieiit as a cycloidal shape, and whose upper surface towards the 

 Ai-uold^ ^ ^ extremity presents to the view a triangular form, two sides of 

 which are described by right lines, and the other by a cycloi- 

 dal curve, which is the principal part of action. 



In this plan the whole of the escapement wheel is thrown 

 open to view ; BBd the escapement or locking spring, 

 screwed fast by its end C to the pillar D, and extending 

 from C to f/ in the direction CBNBd. The centre of motion 

 of this spring is between C and N, the part NBcl being more 

 substantial than the part CBN, and into which part between 

 JSf and B is fixed the locking piece a, the locking piece or 

 locking pallat, whose acting surface is a jewel (see also Fig, 

 4,) placed between N and B and opposite the end of an 

 adjusting screw .f, which pallat descending from the escape- 

 ment spring, locks upon the interior angle of the tooth 2, and 

 upon every tooth in succession, suspending the motion of the 

 escapement wheel for a time, and leaving the balance to 

 vibrate without interruption from any part of tlie machinery. 

 It is to be observed, that the triangular parts of the teeth of 

 the wheel AAA, the wheel being hollowed or sunk, arc 

 raised above the periphery of the wheel to meet the locking 

 piece a, so that upon viewing the wheel edgewise, see Fig. 5, 

 the teeth will appear broader than the edge of the periphery 

 b. In Fig. 3, the locking pallat a being in contact with the 

 tooth 2, is not so well distinguished as in Figures 6, 7, and S, 

 y/here it appears very plainly over the periphery b, of the 

 wheel in the interval between the teeth 1 ana 2. ^ 



Fig. 4, gives a view of the escapement spring reversed, and 



Figi 9 explains upon a large scale the figure of the locking 



,; piece, which is angular, adjoining that part of the strjiight 



edge 



