ON TIMEREXCPEKS.

193

Notwithstanding all possible precautions in the immediate application of theWeight 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 leverto a given height, whence it may descend; and in watches, by bending as P'ing into a given position, from which it may return, so as to limit withgreat precision the propelling force employed in each vibration. The ne-cessity of applying oil is sometimes .in great measure removed by jewellingholes in which the axes or verges run; a perforation being made in aplate ot ruby, and a diamond applied upon this, in contact with the end of theaxis ; the hardness and high polish of these stones tending very considerably*° diminish the friction.

There are also different methods of continuing the action of the force,' v hile the clock or watch is wound up: a spring is interposed between theftisee and the wheel impelled by it, a little inferior in force to the original"eight or spring, so as to remain always bent, until, when the pressure of^e main spring is removed, it begins to act upon a fixed point on one side,^ u d upon the wheel of the fusee on the other, so that it propels the work01 a short time Avith a force nearly equal to that of the main spring. Some-* ailCs also the spring is wound up by causing a small wheel to revolve rounde centre of the fusee,having its teeth engaged on one side in those of a wheel*ich makes a part of the fusee, and on the other side with the internal teetha hoop connected with the work, so that the same pressure which winds'P the spring tends also to turn the hoop round, and to continue the motion.>i;ite XVI." Fig. 200.)

I he scapement, by which the sustaining force is communicated to the pen-u mm or balance, demands a greater exertion of skill and accuracy than anyj ler part of a timekeeper. Sometimes the alternate motion of the pendu-111 has been produced by the action of a crank, but this construction sub-c s it too much to the irregularities of the wheel work, and is liable to se-otner objections. A crank cannot properly be called a scapement, forj.j^ f)r( hig to the etymology of the term, the pendulum must escape for ale from the action of the wheehvork, and in general, the more indepen-

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