tiSO NATURAL THEOLOGY. 



the pendulum. The notched wheel below is the 

 scapement-wheel ; two projecting pallets on dif- 

 ferent faces of the axle of the balance-wheel fall 

 in succession between the teeth of the scapement- 

 wheel ; when one of these slips off the teeth, and 

 the axle is set free, the spring recoils, and delivers 

 the other pallet into the succeeding notch: and 

 thus the regular motion of the spring, without 

 stopping the revolution of the scapement, regulates 

 the time in which the teeth are let loose, and by 

 this means equalizes the motion of all the wheels. 



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Here is another form of the scapement-wheel. 

 Call the upper part the crutch, the lower the 

 scapement-wheel. The sustaining force, which, in 

 this instance, is the spring, operating through a 

 succession of wheels, throws out the pallet of the 

 crutch from the tooth of the scapement : in doing 

 this the teeth act against a hair-spring, which, by 

 its recoil, places the pallet in the succeeding 

 notch. By this contrivance the regular motion of 

 the hair-spring corrects the lesser deviation in the 

 motion of the wheels which might otherwise arise 

 from the imperfection of the workmanship. The 

 balance-wheel and spring move with a quickness 

 which permits the scapement-wheel to beat 18,00t> 



