INVENTION OF CHRONOMETERS, &C. 291 



cliiied plane, over which the pin slides with little resistance, and 



W'ithout disturbing the c'otent. At the next vibration, the detent 



as disengaged, a new impulse is communicated as before ; and 



the actions, already explained, continue to be performed in 



succession. 



F. Berthoud thinks that construction the simplest and safest The same es- 



in practice, and gives it again as such in his later works,* with ^apement a 



' . . " htcle varied by 



fl. uttle alteration in the arrangement of the pieces, as represent- Berthoud. it 



ed in Fig. 11, which is copied from Fig. 0, Plate XI IT. of the ^^^s thel,ack 



° ^ o -/» spring and 



Htstoire de la Mesiire du Temps.f In this construction, Berthoud an unlocking 

 attached a very delioate spring to the outside of the arm, 7i j spring, 

 which, projecting a little beyond the extremity ,^ serves for the 

 purpose of yielding in one vibration, and unlocking the detent 

 in the next, instead of rendering the arm itself flexible. The 

 additional arm, k, is only intended to stop the wheel, when the 

 balance is taken out ; and the other parts of the figure, after 

 what has been said in the preceding paragraph, need no farther 

 explanation. 



In the construction of the detached escapement adopted by observation 



Berthoud, the impulse of the escape wheel is communicated to \^^^^ Berthoud 



^ ' '^ has not given 



the balance, not on the circumference of the balance, as in Le his imptilse to 



Roy's second escapement, but on a circle, or pallet, situated *!^^ balance 

 considerably nearer the axis, as in the former escapement, jected springs,' 

 The detent also acts by means of springs, as in Le Ptoy's first ^® ^^ ^'^'^ ^^^' 

 plan, and not by the sort of mechanism which that author 

 thought preferable. On these two points, the practice of suc- 

 ceeding watchmakers has continued in conformity with those 

 two retrograde steps ; but, whether on account of real advan- 

 tages, or merely from the greater facility of execution, need •*' 

 not, on the present occasion, be discussed. 



We come now to the constructions used at present, by the English con- 

 English watchmakers; and shall begin with that of the late fj^'^gg^"^"/ 

 Mr. Arnold, as described inhjs statement, presented by his son ments. 

 to the Board of Longitude. 



* De la Mesure du Temps, ou Supplement au Traite de Ilorloges 

 Marines, &c, 1787, chap. iv. — Histoire de la Mesure du Temps, ' 

 1802, vol. ii. pp. 32 and 33. 



t See also Fig. 8. Plate IV. of the Supplement au Traite des 

 Ilorloges Marines. 



P p 2 Tha 



