A machine for ascertaining the weights of bodies, usually denominated the Roman balance. It consists of a lever of unequal arms, suspended horizontally; to the shorter of the two arms is suspended the article to be weighed, and on the longer arm a weight is made to traverse, until the beam rests in a horizontal position; the position of the traversing weight indicating the weight of the article, which is engraved on the beam where the weight stops. See the articles Balance and Lever. There is, however, another kind of steelyards in extensive use for domestic and other purposes, wherein great nicety in weighing is not appreciated. They are usually called "pocketsteelyards," and are thus constructed: - In the centre of a distended spiral spring of many coils, is a metallic bar, on which are marked the divisions of the scale, according to the amount of force or weight in pounds, requisite to compress the spring to any point represented. To one end of the bar is rivetted a plate, to press upon the spring, which are both in a cylindrical metal case; the other end of the bar passes freely through a hole in the bottom flat end of the case, where it is connected to a hook, on which the article or goods to be weighed are hung; and according to their actual weight the bar, by compressing the spring, is externally protruded, showing by the figure on the scale the weight of substance suspended.
A great variety of machines for indicating weight and pressure by the elastic resistance of springs have been invented, and several have been described in the course of this work, (see the articles Dynamometer, Cable, and others,) and we shall here add one more, which has been brought into very extensive use by the diligence and skill of Mr. Marriott, of London. The machine we allude to is denominated Marriott's Patent Weighing Machine. It is an invention of 150 years standing, and the improvements made by Mr. Marriott relate to some minutiae, which, though of a subordinate, are not of a useless character. The annexed diagram is illustrative of the construction of the internal part. a is the ring by which the machine is suspended: to the stem proceeding from the ring the uppermost side of a strong elliptical steel spring is made fast by a nut and screw; at b is suspended the scale, or other receptacle to hold the goods to be weighed; the stem of this is secured to the lowermost side of the spring, and likewise at its upper extremity to a vertical rack c, which is drawn downwards as the elasticity of the spring is operated upon by the weight; the descent of the rack turns a small toothed pinion d, on the axis of which is fixed a hand e, that points out upon the graduated circle f, the amount of the force or weight applied.
The inner circle g, shows the periphery of the circular box, which encloses the parts delineated within it. The periphery of the front plate and the index are shown in dotted lines, as they are not supposed to be seen in this view of the apparatus. This machine is extremely convenient and portable, it requires no weight, may be hung up any where, and is. sufficiently accurate for the generality of purposes, where inaccuracies to the extent of a few small fractional parts are of no moment.