The Pendulous-Weight Letter Scale: A Steelyard With a Straight Arm, a Weight Below to Keep the Plate Level

"In the drawings, A, represents the foundation or base for supporting the operative parts. From the said base part, two vertical standards, or columns, B, C, extend upward and have mortises, a, b, made respectively in their top parts, the same being for the reception of a wedge or knife shaped bar, D, whose ends, c, d, rest respectively in the said mortises. The said bar, D, passes transversely through the graduated arm, E, and serves as a fulcrum for it, such arm being provided with divisions, to mark either the whole ounces, or fractions of the same" "In my construction of scale, I make the weighing lever or steelyard without any bifurcation or fork, but simply as a straight bar provided with knife edges for supporting the bearing of a pendulous weight"

**Base and standards.** Screw two hardwood standards to a base 6 cm apart and file a V notch in the top of each. **Arm and knife-edges.** Cut a 25 cm arm from aluminium flat bar. Drill it near one end and fit a short piece of steel rod filed to a knife-edge across it as the fulcrum D, resting in the notches. Fit a second knife-edge 20 mm behind it as I. **Plate and pendulous weight.** Bend a wire frame H with notched ears that hang on the knife-edge I, fix a small plate F on top of it, and hang a rod from the frame's bottom down through a tube fixed to the base, with a weight on its end as K. **Poise and stop.** Bend a sliding poise N from sheet and wire, and put a wire loop g round the arm's rear on a third standard to limit its tilt. **Calibrate.** With nothing on the plate, add or file weight until the arm balances with the poise at zero. Put calibration weights of 28 g, 57 g and 113 g on the plate in turn, find the poise's balance and mark the arm; check that the marks are equally spaced, as the notebook says. Weigh a letter.

**Thaddeus Fairbanks** of St. Johnsbury, Caledonia County, Vermont, received US 26,026, dated 8 November 1859. The frame's ears h, i were recessed under to take the knife-edged bar I; the rod I′ ran down through the hollow column L to the weight K; the standard M bore the arm's rear on its top, with the loop g against too great an inclination. He did not claim balancing a pan by a pendulous weight on a straight arm, nor a pan on a forked steelyard, but the letter scale with its pendulous weight on a forked arm resting on the knife-edges of a bar extended from a straight steelyard, and the front end extended into a stationary staple. **Honest limits.** Aluminium, wire and filed rod stand in for his made scale. The notebook treats the knife-edges as frictionless points; its lengths and poise are examples. Your calibrated marks are the result.