COMMON THINGS CLOCKS AND WATCHES. 



hammer A receiving the same jerk strikes upon the bell v and 

 instantly recoils from it ; and if the wheel o continues to revolve, 

 one pin after another upon it will encounter the lever 6, and the 

 hammer A will make a stroke upon the bell each time that a pin 

 passes the lever. 



The wheel H is so constructed that it will make one revolution 

 in the interval between two successive strokes of the bell, or 

 what is the same, in the interval between the moments at which 

 two successive pins pass the lever b. 



In the train which moves the hands, an expedient is provided 

 by which each time that the minute hand passes twelve upon the 

 dial, the lever m n is thrown back from the position which it has 

 in fig. 31, and the top m being withdrawn from under the pin 

 upon the wheel JET, that wheel and the entire striking train is 

 liberated and set in motion. At the same time the piece is taken 

 out of the notch in which it rested on the wheel o p t and that 

 wheel, in common with the other parts of the striking train, is put 

 in motion. 



For every complete revolution that the wheel H makes, the 

 hammer A makes a stroke upon the bell, and the motion of H and 

 of the entire striking train will continue until the end m of the 

 lever m n again conies under the pin projecting from the face 

 of n. During the motion, the lever m n is kept back by the 

 edge of the wheel op acting against the piece projecting from the 

 lever m n. But when the wheel o p has turned so as to bring the 

 next notch to the projecting piece, it will be thrown into the notch, 

 and the end m of the lever m n coming under the pin projecting 

 from the wheel H, the motion of the train will be suspended. 



Now, it will be evident from what has been stated, that when 

 the lever m n is thrown back by the works, it is kept back by the 

 edge of the wheel o p acting against the projecting piece, and so 

 long as it is thus kept back, the striking train continues to move 

 and the hammer continues to strike the bell. But the duration 

 of this motion will depend on the space between the notches on 

 the wheel o p, since it is while that space upon the edge passes 

 under the projecting piece on m n that the end m of the lever 

 m n is kept back so as to be out of the way of the pin projecting 

 from the wheel H. These spaces between the notches are there- 

 fore so proportioned, one to another, that the lever m n at each 

 hour is held back a sufficient time for the hammer to make upon 

 the bell the number of strokes denoting the hour and no more. 



The arrangement for striking half-hours and quarters is based 

 upon similar principles. 



48 



