2Q2 INVEJTTION OF CHRONOMETERS, icC. 



Description of The teeth of the escape wheel (Fig. 12, Plate IX.) are of a 

 Arnold's es- cycloidal shape,* in the face part which is intended for action, 

 takes the wheel, the section of which, with those of the two other sides, form a 

 totSof'Le ^°^^ °^ mixed triangle. BBd represents the detent, which is 

 Roy's first es- formed of a flexible piece or spring, bending between C and N ; 

 unKsfbyT'* and in the part tiBd, which is stronger than the other, is 

 pallet, without fixed the locking pallet, a, opposite an adjusting screw F. The 

 ^^*^|^'g^^*",^® pallet, projecting below the spring detent, locks upon the inte- 

 escapement ; rior angle of the tooth ; suspending the motion of the escape 

 add e^"^ i ^'^^^^^> ^^^ leaving the balance to vibrate free, as pointed out 

 of the parts are in the preceding escapements. The action of the spring detent 

 anZthe"teeth' ^^^^ the joint of the detent is itself a spring) presses the locking 

 of the wheel pallet against the screw, F, except at the time of unlocking the 

 fol-m ^ the de!^^^^'^^^* ^ very delicate spring, N e, called the discharging, or 

 tent moves by unlocking spring (and also the tender spring), is attached by 

 ?ns?eSpiV ^"® ^'^^' ^' *^ ^^^ ^P™g detent, CBNB a ; and, passing under 

 vots, and it has the adjusting screw, F, extends a little beyond the extremity, </, 

 Jp'ring."''^'"^ of the detent itself. HHH is a circular piece attached t© the 

 axis of the balance and, o, the discharging pallet. This pallet, 

 ^vhen the balance is in motion from e to d, presses against the 

 end of the discharging spring, n e * and, carrying it together 

 with the locking spring, BBd, disengages the locking piece, 

 a, out of the internal angle of the tooth, with which it was 

 in contact ; and the escape wheel then communicates a new 

 power to the balance, by its impulse on a pallet, w, which is 

 fixed, or set, in the aperture of the circular piece. As soon as 

 this is done, the spring detent, or locking spring, falls back to 

 its position against the adjusting screw, F ; and the pallet, by 

 receiving or intercepting the next tooth, stops the motion of the 

 escape wheel. When the balance returns from d to e, the un- 

 locking pallet acts again on the extremity of the discharging 

 spring, but, this being very delicate, gives way without disturb- 

 ing the detent or locking spring ; and the balance, after suffer^ 

 ing a trifling degree of resistance by that contact, continues its 

 free vibrations. At the next vibration, the unlocking . takes 



* As the descriptions of the escapements for which Arnold and 

 Earnshaw have been rewarded, are not of considerable length in 

 the present interesting communication, I have re-engraved the 

 sketches, instead of referring to Plates 13, vol. xiii. and 2, 3, vol. 

 ijfiv, of our Journal, where the full descriptions arc given.— W. N. 



place 5 



