196' LECTURE XVII. 



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formed as to create a slight recoil; but this construction docs not appear to 

 have been very successful in practice. The friction may, however, be con- 

 siderably diminished by the duplex scapement, apparently so called from the 

 double series of teeth employed. The teeth of the more prominent series are 

 detained on a cylinder so small as to be unfit for receiving an impulse from 

 them, the balance is therefore impelled by the other series of teeth, acting on 

 a pallet at a greater distance from its axis. Tlie French have sometimes em- 

 ployed a construction somewhat similar, which they call the comma scapement, 

 the teeth first resting on a small arch of repose, and then impelling the curved 

 jsurface of a pallet extending to a considerable distance beyond it. In both 

 these cases the single pallet, which is impelled by a tooth of a simple form, 

 requires less labour in the execution than a number of a larger teeth, each of 

 which is to be finished with great accuracy : but watches on these construc- 

 tions, especially those with the comma scapement, are too liable to be stopped 

 by any sudden motion, although the duplex scapement begins to be fre- 

 quently employed for pocket timekeepers. (Plate XVI. Fig. 205.) 



Mr. Harrison avoided all friction on the pallet, by connecting it with the 

 pendulum by means of a slender spring, so flexible as to follow the motion of 

 the scape wheel to a sufficient extent without sliding on its teeth. But the 

 construction which is most usually employed where the greatest accuracy is 

 required, is the detached scapement; in which the teeth of the scape wheel 

 always rest on a detent, exce])ting a short interval, when it is unlocked in 

 order to impel the pallets. Mr. Mudge employed a detached scapement, ac- 

 tuated by a subsidiary spring, of which the force is scarcely liable to any va- 

 riation; the detent being unlocked by the motion of the balance. Mr. Haley 

 has refined still further on this construction, by causing the subsidiary spring- 

 to unlock the wheel in its return, so that the balance is relieved from this ac- 

 tion, which may sometimes produce a slight irregularity. These construc- 

 tions are, however, much too delicate for common ppcket watches. In a 

 clock, Mr. Gumming has employed a detached scapement, in which a lever is 

 raised to a certain height by each tooth of the scape wheel, and acts immedi- 

 ately on the pendulum in its descent in the middle of the vibration. The 

 scape wheel is unlocked by the pendulum during its ascent, and a variation 

 of the pressure may, therefore, produce a very slight inequality in the motion 

 of the pendulum. Mr. Nicholson has attempted to remove this cause of 



