ON TIMEKEEPERS. 193 



Notwithstanding all possible precautions in the immediate application of the 

 weight or spring, the irregular action of the teeth of the wheels, the in- 

 creasing tenacity of the oil usually employed, and other accidental disturb- 

 ances, make it still desirable to procure a further equalisation of the force, 

 which is sometimes obtained in clocks, by raising the loaded arm of a lever 

 to a given height, whence it may descend; and in watches, by bending a 

 spring into a given position,' from which it may return, so as to limit with 

 great precision the propelling force employed in each vibration. The ne- 

 cessity of applying oil is sometimes in great measure removed by jewelling 

 the holes in which the axes or verges run; a perforation being made in a 

 plate of ruby, and a diamond applied upon this, in contact with the end of the 

 axis; the hardness and high polish of these stones tending very considerably 

 to diminish the friction. 



There are also different methods of continuing the action of the force, 

 while the clock or watch is wound up : a spring is interposed between the 

 fusee and the wheel impelled by it, a little inferior in force to the original 

 weight or spring, so as to remain always bent, until, when the pressure of 

 the main spring is removed, it begins to act upon a fixed point on one side, 

 and upon the wheel of the fusee on the other, so that it propels the work 

 for a short time with a force nearly equal to that of the main spring. Some- 

 times also the spring is wound up by causing a small wheel to revolve round 

 the centre of the fusee,having its teeth engaged on one side in those of a wheel 

 which makes a part of the fusee, and on the other side with the internal teeth 

 of a hoop connected with the work , so that the same pressure which winds 

 up the spring tends also to turn the hoop round, and to continue the motion. 

 (PlateXVI. Jig. 200.) 



The scapement, by which the sustaining force is communicated to the pen- 

 dniiim or balance, demands a greater exertion of skill and accuracy than any 

 other part of a timekeeper. Sometimes the alternate motion of the pendu- 

 lum has been produced by the action of a crank, but this construction sub- 

 jects it too much to the irregularities of the Vvdieelwork, and is liable to se- 

 veral other objections. A crank cannot properly be called a scapement, for 

 according to the etymology of the term, the pendulum must escape for a 

 time from the action of the wheelwork, and in general, the more indcpen- 



VOL. I. c c 



