HOROLOGY. 



used by the late Josiah Emery, in his chro- 

 nometers, some of which have gone very 

 well. It differs from the constructions 

 which we have already explained, both 

 in the detent and in the communication 

 of the impulse, which in this mechanism 

 takes place at every vibration : but the 

 date will not suffer us to consider it as the 

 lirst invention of the detached escape- 

 ment. 



This justly celebrated artist afterwards 

 made a chronometer, in which the vibra- 

 tions of balance were kept up by second- 

 ary springs attached to two pallets, each 

 of which was woundup by the last wheel 

 of the train during- the time employed by 

 the balance in its vibration, unconnected 

 with that pallet. Though this invention 

 is highly ingenious, and was rewarded by 

 parliament, it is now generally considered 

 as unsafe in the locking of the hooks, or 

 detent parts, which terminate the pallets. 

 Mr. Alexander Camming executed a si- 

 milar escapement for clocks long before 

 Mudge actually carried his idea into ef- 

 fect, though it has been contended that 

 Mudge had the mere notion much earlier. 

 But Mr. dimming, to whom our art and 

 the other branches of mechanics are 

 highly indebted for his labours, and his 

 Treatise on Clock and Watch Making, 

 made his detents separate from his pal- 

 lets, and by that means avoided the chief 

 defect of the construction afterwards 

 adopted by Mudge. Our limits will not, 

 however, allow us to pursue these and 

 other improvements and variations, adopt- 

 ed by our own and by foreign artists. 



We must confine ourselves to the con- 

 struction used at present by the English 

 watchmakers ; and shall begin with that 

 of the late Mr. Anold, as described in his 

 statement, presented by his son to the 

 board of longitude. 



The teeth of the escape wheel (fig. 5.) 

 are of a cycloidal shape, in the face part, 

 which is intended for action, the section 

 of which, with those of the two other 

 sides, form a sort of mixed triangle. B B d 

 represents the detent, which is formed of 

 a flexible piece or spring, bending be- 

 tween C and N ; and in the part N B d, 

 which is stronger than the other, is fixed 

 the locking pallet, o, opposite an adjust- 

 ing screw F. The pallet, projecting be- 

 low the spring detent, locks upon the in- 

 terior angle of the tooth ; suspending the 

 motion of the escape wheel, and leaving 

 the balance to vibrate free, as pointed out 

 in the preceding escapements. The ac- 

 r.ion of the spring detent (for the joint of 

 the detent is itself a spring) presses the 



locking pallet against the screw, F, ex- 

 cept at the time of unlocking the wheel. 

 A very delicate spring N e, called the 

 discharging or unlocking spring (and al- 

 so the tender spring,) is attached by one 

 end, N, to the spring detent, C B N B o; 

 and, passing under the adjusting screw, 

 F, extends a little beyond the extremity, 

 d, of the detent itself. H H H is a circu- 

 lar piece attached to the axis of the ba- 

 lance, and, o, the discharging pallet. This 

 pallet, when the balance is in motion from 

 e to d, presses against the end of the dis- 

 charging spring, n e ; and carrying it, to- 

 gether with the locking spring, BR d, 

 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, m, 

 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 ad- 

 justing screw, F ; and the pallet, by re- 

 ceiving or intercepting the next tooth, 

 stops the motion of the escape wheel. 

 When the balance re turns from d to e,the 

 unlocking pallet acts again on the extre- 

 mity of the discharging spring ; but this, 

 being very delicate, gives way without 

 disturbing the detent or locking spring ; 

 and the balance, after suffering a trifling 

 degree of resistance by that contact, con- 

 tinues its free vibrations. At the next vi- 

 bration the unlocking takes place ; and 

 the action of the escapement proceeds 

 successively, as explained before. 



The detached escapement used by Mr. 

 Earnshaw, is represented in fig. 6, which 

 is taken from his statement presented to 

 the board of longitude. This escapement 

 is similar to that of Arnold's, already de- 

 scribed, except in small variations, which 

 will be easily perceived on a comparison 

 of the two figures. It is besides asserted, 

 and it appears probable from every cir- 

 cumstance relative to these constructions, 

 that the late Mr. Arnold had made use of 

 this form of escapement long before Mr. 

 Earnshaw, but that he had laid it aside, in 

 order to adopt the escapement with cy. 

 cloidal teeth, which he esteemed far pre- 

 ferable. In the escapement we are now 

 considering, the escape wheel is shaped 

 as appears in the figure ; and, on the in- 

 spection of this representation, it will be 

 easily observed, that the teeth presenting 

 a right line, and escaping by a sharp point, 

 their action cannot be so smooth, and the 

 wear of the whotemust be greater, than in 

 the construction with protuberant cycloid- 

 al teeth. The detent is of the same kind as 



