Images(3)

revolving copper disk

Date1850-1870

Inventory Number0495

ClassificationBarlow's wheel

Subject

Maker American ?

User Department of Physics, Harvard University founded 1884

Cultural Region

Place of Use

Dimensions30 × 22.9 × 15.4 cm (11 13/16 × 9 × 6 1/16 in.)

Material

DescriptionA thin copper disc held vertically. The disc has a notably stained rim. It is held up by pivots, allowing it to rotate. The rim at the very bottom of the disc dips into a very shallow trough, made of a black metal, which would be filled with mercury. A thin horseshoe magnet is mounted vertically, perpendicular to the copper disc. The poles of the magnet rise up just below the pivots on the disc. Both the metal stand for the trough and the magnet are mounted on a rectangular wooden base with rounded, beveled angles. Two binding posts are on either end of the base. The base rests on four rectangular feet.

Signedunsigned

Inscribedon base, in white paint: E2

Curatorial RemarksFrom Fred Schewler. Stamped 8-70 (ca 1870); "Oval tag" 6-4-10 (ca 1880). "E2" in white paint (ca 1920), indicating Electric Shelf 2 in Jefferson Demonstration Cabinet.

FunctionThis instrument was meant to demonstrate a homopolar motor. A power source, connected via one of the binding posts, would pass an electric current to the hub of the copper disc. The rim of the disc sits in the mercury-filled trough. Because mercury conducts current, the electricity would run from the hub to the rim to the mercury. The other contact to the power source is connected to the mercury. With the circuit closed, and the current flowing, the surrounding U-shaped magnet and its resultant field cause the disc to rotate.

ProvenanceFrom the Department of Physics, Jefferson Laboratory, Harvard University.