49.5
Brass
INDEX 1788 : C.V.110
Statera Romana cum sacomate ex orichalco.
Roman balance with a brass counterbalance.
This is one of the two examples of small steelyards, which show the mechanism of the inter-fixed lever with unequal arms. The longer arm measures 39 cm and is equipped with a cursor-weight which moves along it in order to achieve equilibrium. This arm, which has a quadrangular cross section, has two different scales which are engraved along two opposite sides. One of the scales shows 112 divisions, not numbered, with large strokes in divisions of 4 and smaller ones in between these. The intermediate demarcations are composed of even smaller strokes. The other graduation has 128 divisions, also without numbers, with large strokes in intervals of 4 and smaller ones for all of the other graduations. There are then two independent graduations, owing to the fact that this steelyard can be suspended by two hooks. According to the choice made, there will be different relationships between the lengths of the longer and smaller arms of the lever, corresponding to different scales.
The fact that each principal division was subdivided in 4 parts, suggests that the unit of measurement was the pound, 4 ounces corresponding to each quarter division, since 1 pound equals 16 ounces. As for the sliding weight, it is not possible to determine which of the existing weights in the Gabinete de Física was originally part of this instrument.
From Colégio dos Nobres, catalogue n.º 102.
´s Gravesande, Willem Jacob, Physices Elementa, Leiden, 1742, Vol. I, § 194, Tab. VI, fig 4.