Mechanics. igi

z. The Manner in which a Weight acts upon theCylinder, about which the Line or Cord (to which ithangs) is wound, is easy to be understood by all; butthe Action of the Spring coi'i’d up within the CylindricBarrel or Box of a Clock or Watch, is somewhat morenice and mysterious ; and the Manner how it acts uponthe Fusee always with an equal Force by means of theChain, and the proper Figure of the Fusee for thatPurpose, is next to be explain’d.

4. The Chain being fix’d at one End to the Fusee,and at the other to the Barrel, when the Machine i»winding up the Fusee is turn’d round, and of course theBarrel; on the Inside of the Barrel is fix’d one End ofthe Spring, the other End being fix’d to an immove-able Axis in the Centre. As the Barrel moves round,it coils the Spring several Times about the Axis, there-by increasing its elastic Force to a proper Degree ; allthis while the Chain is drawn off the Barrel upon theFusee ; and then when the Instrument is wound up, theSpring by its elastic Force, endeavouring constantly tounbend itself, acts upon the Barrel, by carrying itround; by which means the Chain is drawn off fromthe Fusee, and thus turns the Fusee, and consequentlythe whole Machinery.

5. Now as the Spring unbends by Degrees, its elasticForce, by whi.h it affects the Fusee, will gradually de-crease; and therefore unless there were some Mechani-cal Contrivance in the Figure of the Superficies of theFusee to cause that as the Spring is weaker, the Chainshall be removed farther from the Centre of the Fusce,so that what is lost in the Spring’s Elasticity is gained inthe Length of the Lever; I fay, unless it were for thisContrivance the Spring’s Force would always be une-qual upon the Fusee, and so would produce an un-equable Motion of the Parts of the Machine.

6. The Figure of the Curve, which fir all form the pjSuperficies of the Fusee by a Revolution about its Axis, j 'may be investigated as follows. Let BCD be the °Curve, AL the Axis of the Fusee produced ; let D be

the Point where the End of the Chain is fix’d on theFusee when the Watch is down, or the Spring un-coil’d, and B the Point where it touches it when the

Spring