INVENTJON OF CHRONOMETERS, 6iC. 28^ 



a line drawn from that point to the centre of the balance would 

 form with the curve, A E, a mixed angle of about 80°. QPG is 

 an angular lever, turning on pivots at P, the branch of which, 

 PX, when in contact with one of the teeth of the escap* 

 wheel, stops its motion ; and the spring, RM, tends to keep it 

 ilisengaged against the pin K. The effect of this construction 

 is as follows : 



Suppose the action of the tooth, D, of the escape wheel to The effector 

 give tension to the spiral spring, and make the balance move rov's escape- 

 round an arc more or less extensive ; the end, C, of the half- rtient. 

 cylinder or roller, at the same time, pushes the angular lever, ^vheel is kept 

 Q P X, by its end, Q, making the end of the branch, P Q, rest »" repose by a 

 upon the circumference of IC; and when the tooth, D, quits The balance 



the pallet, A E, the tooth, G, comes in contact with the end, X, ""locks the d^- 



, . , , . tent and re- 



wmch then contmues the motion of the angular piece, Q M X, ceives an im- 



till the tooth and the end, X, are completely engaged and re- P"^^'^ *^^,^'^''°'^® 



' ^09 Qjj ^ pallet 



main at rest. In this situation, no part of the branch, P Q, thro' a part of 



touches the round part, C I ; and the balance proceeds in its every second 



. . Vibration ; and 



vibration as if it were insulated. Its velocity being soon destroy- during great 



ed, by giving tension to the spiral spring, the reaction of this P^*"* *^^.'*-f ^ 



' -^ * ^ 1 r o» course it IS free 



spring brings it back with an accelerated motion, and at the and detached. 



§econd vibration the pallet, A E, comes into contact with the 

 escape wheel, and by its action on the tooth next following D, 

 causes the wheel to recoil, by a space, which may be equal to 

 half the distance between two teeth. The branch, X, of the 

 lever, in consequence of that motion, becomes disengaged out of 

 the teeth of the wheel, and, by the action of the spring, R M, 

 falls against the ])in, K ; after which, the escape wheel gives a 

 new impulse to the balance, pushing the pallet, D E, in the con- 

 trary direction; and the vibrations proceed alternately, in the 

 manner explained before. 



While we give this escapement as the first of that kind ever u has been as- 

 invented, it is proper to remark, that according to report,* ^^'"*'^<^'' l^"* "o'= 



. . , proved, that 



Jean Baptiste Dutertre, the elder, a very skiltul watchmaker Dutertre in- 



at Paris, in the beginning of the last century, had thought of, ^e'lted a de- 



.,, -Till , , • • tached escape=. 



or actually contrived, a detached escapement ; but as his inven- ment earlier 



than L« Roy, 



* Traite des Horloges Marines, par F. Berthoud, 1773, p. 97. 

 Etrennes Chronometriques poiu" i'annee, 1759, par P, le Hoy, p. 

 88. 



tioD, 



