WEIGHING-MACHINES are of various forms according to the quantity and species of the goods whose weight is to be determined. The great majority of weighing-machines are founded upon the principle of the lever (q.v.), the chief exceptions being the various forms of the spring-balance (q.v.), to which might be added (though iu such cases the term "machine" is quite inapplicable) some of the methods employed to determine specific gravity, time of oscillation, etc. The simplest and primitive form of weighing machine is the balance (q.v.) with equal arms, which can be adapted either to the maxi mum of accurate weighing or to the most rapid equipouderance. But as this machine necessitates the placing in one scale of weights equal to the weight of the goods, it was soon found to be more convenient to employ is lever with unequal arms—the goods to be placed in the scale attached to the short arm, and therefore equipoised by less weights, the ratio of the weights in the two scales being in proportion to the ratio of length of the arms. On this principle the steelyard (see BALANCE), the bent lever balance (see BALANCE), and the cart-steelyard are constructed. But the convenience of equipois ing a greater weight by one much less is counterbalanced by a considerable diminution in accuracy—one of the causes of error being the greater haoility to flexure of the longer arm of the lever; and another, the necessity, for convenience' sake, of having the arm which is affected by the goods to be weighed as short as possible—the latter of itself reducing the accuracy of the steelyard to that of a symmetrical balance, whose arms lire; each equal to the short arm of the steelyard. However, on behalf of the steelyard, there
is again the advantage of rapid equipoise. Each of these machines is variously con strneted, the modifications having reference either to convenience of use, or to the species or weight of the goods to be weighed: an example of the former is the equal armed balanced, made in an inverted manner, with the scales above, and the rods which connect the scales with the beam so united as to preserve their perpendicularity during oscillation; and the latter is appropriately illustrated by the form of cart-steelyard given in fig. 1. The dotted lines, DD, HD, indicate the grooved plates on which the wheels rest; E, E, E, E are the four points supporting the wheel-plates on the two triangular levers, CBB, CBB; the triangular levers are sup ported by the hooked extremities of their bases, B, B, B, B, upon fixed supports, A, A, A, A; while their ver tices, C, C, are attached to a lever, FG, whose fulcrum is at F; G is attached by a chain to H, the extremity of a lever of the first kind, whose fixed support is at K., and on whose other arm (graduated) the weight for equipoising the cart and its load are placed. The machine is thus seen to be compound, consisting of the two triangular lever pieces, of a simple lever of the second, and of one of the first kind; the weight L, if sufficient, raising II, and with it G, and thence raising C, and so balancing the downward pressure of the cart and its load at B, E, E, E. Various other forms of the cart-steelyard are in use. Mr. Duckliam's weighing-machine is an ingenious adaptation of liv(rrostaties,