dynamometer strain gauge
Date: 1830-1840
Inventory Number: DW0899
Classification: Dynamometer
Dimensions:6 x 22.8 x 31.6 cm (2 3/8 x 9 x 12 7/16 in.)
case: 8.5 × 43.6 × 28 cm (3 3/8 × 17 3/16 × 11 in.)
blue board box: 13.3 × 48.6 × 33 cm (5 1/4 × 19 1/8 × 13 in.)
Accessories: magnets (2); wooden handle with hook; case
DescriptionHeavy elliptical steel loop, which serves as a spring, linked to quarter-circular brass scale through a lever. A rounded y-shaped piece is screwed onto three short pillars on the scale. A steel pointer pivots on a rivet on the y-shaped piece.
The loop is flattened on the longer sides and thickened on the shorter side. The top half is bolted to the back of the scale. The bottom half is connected by a rivet to a lever system that sits behind the y-shaped piece. The lever consists of three arms. The first arm connects to the second via a rigid screw. The second arm is shorter and is connected to the third arm in such a way that the angle between the two arms does not change when pushed. Rather, the pair turns when the first arm pushes against the second arm. The third arm is the needle, which turns on the scale. This needle has a slight protrusion by which it catches the second needle and pushes it. The second needle remains fixed even after the spring is released.
The scale is divided into three different units of measurement. It is numbered from 0 to 280 in myrigrams (10 kilograms), from 0-5600 in livres, and 0-440 in kilograms.
Two O-shaped magnets each have a removable piece in one side. A hook with a turned wood handle is also included.
Steel probably made by puddling method and therefore not uniform in texture.
Device is kept in a leather-covered, chamois-lined fitted case.
Signedin center of top piece covering needle housing: Dynamomètre / par Arnheiter, Bté du Roi / à Paris
Inscribedto left of to numerical scale: Echelle de Tirage
to right of numerical scale: Myria^es / Livres / Kilos
directly under numerical scale, horizontal writing: Echelle de Pression
directly under numerical scale, vertical writing next to a **punctuation symbol** denoting a range 50-60: Force Ordre **??** des Mains
FunctionThis dynamometer is similar to the dynamometer invented by Regnier in 1798 for measuring human and animal strength. The elliptical metal spring would be used in two ways, to determine the strength of a hand's grip by squeezing the spring, or by measuring other back strength by pulling on the spring lengthwise.
In the case of the latter, one side of the spring would be fastened to a fixed object and the other would be gripped by the wooden hook (present), a horse's bridle, or anything else whose strength the user was trying to measure. The "Echelle de Pression" would measure the strength with which the user compressed the spring, the "Echelle de Tirage" measured the strength with which the user could pull the spring in the other direction.
A system of levers transferred the deformation of the spring to the dial on the scale. The bottom part of the spring would push against the first arm of the lever, which would push up on one end of the arm of the second lever, the fulcrum of which is at the point where the arm connects with the needle. This would serve as a bell-crank lever, where the angle between the two would not change but their position would. The needle would push against a second needle, which would remain in the position it was pushed to even after the pressure was released. Most likely, this was used to establish a maximum.
According to H.E. Hoff and L.A. Geddes, Regnier's dynamometer had military applications as well. An official memorandum from 1798 from the French Central Committee on Artillery found the instrument useful in their studies of the force required to start gun carriages.
Primary SourcesE. Regnier, "Description and Use of the Dynamometer, or Instrument for ascertaining the relative Strength of Men and Animals. Invented by Cit. Regnier" Philosophical Magazine 1 (June 1798): 399.
ProvenanceFrom A. Brieux, Paris, July 13, 1962.