178 



DESCRIPTION OF A CLOCK ESCAPEMENT- 



axis of the swing wheel, or last wheel of the train of the 

 clock : b d is the swing wheel fixed upon it, having 30 ser- 

 rated teeth, it is turned round in the direction from 6 to d 9 

 by the maintaing power of the clock, (in the model this 

 power is supplied by the descent of a small weight attached 

 to the end of the small line, which is coiled round the bar- 

 rel y, on the axis of the swing wheel) ; g is a spring detent, 

 which locks against one of the teeth of the swing wheel, and 

 this prevents its running down, by the action of the main- 

 taining power; h is another spring detent, which is called 

 the impelling spring, when left at liberty, it unlocks the 

 former by pushing against the end of the small arch, fig. % 

 e, fastened to the detent g, and thus removing the end of 

 the detent which obstructed the wheel's motion ; / is the rod 

 of the pendulum suspended by a cock screwed to the back 

 plate of the clock; a smart" piece of brass A;, fig. 1, projects 

 at right angles from the impelling spring A, so as to inter- 

 cept the pendulum rod in its vibration, and at this place a 

 small screw is put through the pendulum rod /, the point of 

 which moves the impelling spring back ; a small pin is* 

 fixed to the frame in a line between the point of suspen* 

 sien of the pendulum, and in the centre of the swing 

 wheel, against which the impelling spring stops when at 

 liberty, 

 Theaction Supposing the pendulum to he vibrating backwards and 



forwards, and the wheel locked as in the figure, the pendu- 

 lum swinging from m to n, fig. 2, the impelling spring h 

 follows by its elasticity, until the pendulum I arrives at the 

 perpendicular: at this period the impelling spring comes to 

 rest against the end of the arc e, which it pushes back, so 

 as to release the tooth of the wheel from the detent spring 

 g ; the wheel now moves round a very small space before 

 it meets the end of the impelling spring A, and is stopped 

 thereby, in the mean time the pendulum continues its mo- 

 tion the extent of its vibration towards n, when it returns, 

 and arriving at the perpendicular, it meets the impelling 

 spring A, and carries it along with it, until the tooth of the 

 wheel which rests against it, escapes from the end of it, and 

 another tooth of the wheel comes to rest against the spring 



detent 



