DUPLEX ESCAPEMENT. 



the balance-wheel the small quantity of force which it lost by the 

 previous reaction of the tooth upon its convex surface. 



The side A E of the semicylinder is now thrown before the 

 tooth c, the point of which having advanced through a space 

 equal to the diameter of the semicylinder, is thrown against the 

 concave surface of A E, as shown in fig. 24. 



The balance-wheel now swinging again from right to left, the 

 point of the tooth c slides upon the concave surface of the semi- 

 cylinder A E, until the edge E comes to it. The tooth then slips 

 over the inclined face of E, and in doing so gives the semicylinder 

 and consequently the balance-wheel another slight impulse, 

 restoring to it the force of which it deprived it while previously 

 sliding upon its concave -side. 



The explanation here given of the action of this form of escapement 

 is well calculated to render the conditions which all escapements 

 should fulfil intelligible. These arrangements are primarily 

 directed to the regulation of the movement of the wheel- work, so 

 as to secure its uniformity. This will obviously be accomplished 

 provided that the escapement, whatever be its form, lets a tooth 

 of the wheel pass for each oscillation of the balance-wheel. But 

 owing to the friction of the axis of the balance-wheel, and of the 

 pallets on the teeth of the escapement- wheel, and the resistance 

 of the air, the range of its oscillations would be gradually 

 diminished, so that at last it would not be sufficient to allow the 

 successive passage of the teeth of the escapement- wheel, and the 

 watch would stop unless some adequate means are provided by 

 which the balance-wheel shall receive from the mainspring 

 through the escapement-wheel as much force as it thus loses, 

 All escapements accomplish this by the peculiar forms given to 

 the edges of the pallets and the teeth of the escapement- wheel. 

 In the present case, the object is attained by making the edge D 

 round and the edge E inclined, and by giving to the teeth the 

 form shown in the figure. 



This form of escapement supplies a sufficiently good regulating 

 power for the best sorts of pocket watches, and is attended with 

 the advantages of allowing the works to be compressed within a 

 very small thickness. It is the form most commonly used in the 

 French and Swiss watches. 



41. The form of escapement used in the best English made 

 watches consists of an escapement-wheel, which partakes at once 

 of the double characters of a spur and crown-wheel, and is hence 

 called the duplex escapement. 



The spur teeth, A, B, c, &c. (fig. 25), are similar in their form 

 and arrangement to those of the cylindrical escapement described 

 above. The crown teeth, a, b, c, &c., project from the face of 



37 



