FUSEE

In Watch-work, that part of the machinery about which the chain is wound, and which is immediately acted upon by the mainspring. The use of the fusee is to equalize the action of the spring. In proportion as the spring becomes unwound, its effort continually relaxes; so that if the first wheel were attached to the barrel, as is often the case in common watches, the inequality of the: impelling power would produce a corresponding inequality in the rate of going. In order to correct this, one end of the chain is attached to and wound round the barrel in which the main-spring is contained; while the other end is coiled about the fusee, which has a conical shape, and is fixed on the axis of the first wheel. The principle generally adopted for determining the figure of the fusee is, that its radius, at any point to which the chain is a tangent, should be inversely as the tension of the chain iu that position. Within certain limits this is true; and if we a ume with llooke that the force of a spring is proportional to the distance to which it is drawn from the position of rest, and also lay aside all consideration of the length of the chain wrapped about the fusee, it would be easy to show that the fusee should be the solid generated by the revolution of the equilateral hyperbola about its asymptote. This conclusion is, however, by no means correct; but though the subject has been treated by several eminent mathematicians, very little practical advantage has been derived from the theoretical investigations.Infact, a moderate approximation to the true figure (whatever that may be) is all that can be attained in practice, and all that is nece ary. [s. 498]