90 CHRONOMETERS. 



pendulum. When the cord upon which the weight 

 is suspended is entirely run down from off the 

 barrel, it is wound up again by a key which goes 

 on the square end of the arbor at Q, by turning it 

 in a contrary direction to that in which the weight 

 descends. For this purpose, the inclined side of 

 the teeth of the wheel R (Fig. 2.) removes the 

 click C, so that the ratchet-wheel R turns while 

 the wheel D is at rest; but as soon as the cord is 

 wound up, the click falls in between the teeth of the 

 wheel D, and the right side of the teeth again acts 

 upon the end of the click, which obliges the wheel D 

 to turn along with the barrel; and the spring Akeeps 

 the click between the teeth of the ratchet-wheel R. 

 In portable table clocks and watches, the moving 

 power, instead of being a weight, is a spring, which 

 is coiled up in a spiral manner within a barrel 

 that is connected with a fusee by means of a 

 chain. The chainbeing fixed atone end of the fusee, 

 and at the other to the barrel, when the machine 

 is winding up, the fusee is turned round, and of course 

 the barrel, on the inside of which is fixed one end 

 of the spring, the other end being fixed to an im- 

 moveable axis in the centre. As the barrel moves 

 round, it coils the spring several times about the 

 axis, thereby increasing its elastic force to a proper 

 degree: all this while the chain is drawn off the 

 barrel upon the fusee ; and then, when the instru- 

 ment is wound up, the spring, by its elastic force, 

 endeavouring constantly to unbend itself, acts upon 

 the barrel, and carries it round; by which the 

 chain is drawn off from the fusee, and thus turns 

 it, and consequently the whole machinery. Now, 

 as the spring unbends itself by degrees, its elastic 

 force, by which it affects the fusee, will gradually 

 decrease; and, therefore, unless there was some me- 



