Images(3)

Graham or dead-beat escapement model

Date1839-1850

Inventory Number1994-1-0012

ClassificationEscapement Model

Subject

Maker William Mason Stiles (I) fl. 1824 - 1850

Cultural Region

Place of Origin

Dimensions123 x 31 x 37 cm (48 7/16 x 12 3/16 x 14 9/16 in.)

Material

DescriptionA triangular base that holds the three vertical legs of a tall table on which rests a clock mechanism. The mechanism consists of a brass dented wheel with a spool around its axis that has some string wound around it connected to two weights. Atop the dented wheel is a verge in the form of an arch with two arms that interlock with the dented gear. The verge is pivoted at its uppermost part, where it is connected to a long pendulum that extends downwards almost touching the base.
The base has brass leveling screws.

Stamped with an old Harvard number, "19 56". on two of three wooden legs supporting the escapement.

In Collection(s)

Clocks and Watches

Signedon back brace: W. M. Stiles / Seward St. Goswell St. / London

FunctionThis is a model that demonstrates the escapement device of certain clocks called the Graham or dead-beat escapement. It works by the interaction of a dented wheel with a curved verge with two arms that interlock with the wheel. In one cycle, a locked arm is pushed by the wheel (driven by the weights wound around its axis) in one direction and radially outwards, which causes the opposite arm to move inwards to eventually block the wheel's rotation. There, further force by the wheel causes the verge to swing in the opposite direction completing the cycle. The speed of the oscillations is controlled by the pendulum attached to the verge and the geometry of the surfaces where the verge and the wheel make contact, and each cycle gives the pendulum a push to keep swinging with the same amplitude.

See an animation of a Graham wheel in this website.

ProvenanceAllston Burr Hall (former undergraduate Science Center), Harvard University; transferred to CHSI December 12, 1994.

Historical AttributesUsed in the 19th century for teaching Harvard College students.