STEELYARD

, or Stilyard, in Mechanics, a kind of balance, called also, Statera Romana, or the Roman Balance, by means of which the weights of different bodies are discovered by using one single weight only.

The common Steelyard consists of an iron beam AB, | in which is assumed a point at pleasure, as C, on which is raised a perpendicular CD. On the shorter arm AC is hung a scale or bason to receive the bodies weighed: the moveable weight I is shifted backward and forward on the beam, till it be a counterbalance to 1, 2, 3, 4, &c pounds placed in the scale; and the points are noted where the constant weight I weighs, as 1, 2, 3, 4, &c pounds. From this construction of the Steelyard, the manner of using it is evident. But the instrument is very liable to deceit, and therefore is not much used in ordinary commerce.

Chinese Steelyard. The Chinese carry this Statera about them to weigh their gems, and other things of value. The beam or yard is a small rod of wood or ivory, about a foot in length: upon this are three rules of measure, made of a fine silver-studded work; they all begin from the end of the beam, whence the first is extended 8 inches, the second 6 1/2, the third 8 1/2. The first is the European measure, the other two seem to be Chinese measures. At the other end of the yard hangs a round scale, and at three several distances from this end are fastened so many slender strings, as different points of suspension. The first distance makes 1 3/5 or 8/5 of an inch, the second 3 1/5 or double the first, and the third 4 4/5 or triple of the first. When they weigh any thing, they hold up the yard by some one of these strings, and hang a sealed weight, of about 1 1/4OZ troy weight, upon the respective divisions of the rule, as the thing requires. Grew's Museum, pa. 369.

Spring Steelyard, is a kind of portable balance, serving to weigh any matter, from 1 to about 40 pounds.

It is composed of a brass or iron tube, into which goes a rod, and about that is wound a spring of tempered steel in a spiral form. On this rod are the divisions of pounds and parts of pounds, which are made by successively hanging on, to a hook fastened to the other end, 1, 2, 3, 4, &c, pounds.

Now the spring being fastened by a screw to the bottom of the rod; the greater the weight is that is hung upon the hook, the more will the spring be contracted, and consequently a greater part of the rod will come out of the tube; the proportions or quantities of which greater weights are indicated by the figures appearing against the extremity of the tube.

Steelyard-Swing. In the Philos. Trans. (no. 462, sect. 5) is given an account of a Steelyard swing, proposed as a mechanical method for assisting children labouring under deformities, owing to the contraction of the muscles on one side of the body. The crooked person is suspended with cords under his arm, and these are placed at equal distances from the centre of the beam. It is supposed that the gravity of the body will affect the contracted side, so as to put the muscles upon the stretch; and hence by degrees the defect may be remedied.