Images(6)

electromagnetic loop

Datecirca 1860

Inventory NumberDW0477

ClassificationElectromagnetic Apparatus

Subject

Maker Marc François Louis Secretan 1804 - 1867

Maker Secretan founded 1855

Cultural Region

Place of Origin

Dimensions45 × 35 × 23.8 cm (17 11/16 × 13 3/4 × 9 3/8 in.)

Material

DescriptionA rectangular loop of thick copper wire suspended from brass cups which would be filled with mercury. The cups are mounted on a frame consisting of two brass pillars with binding posts at the bottom, a copper cross piece at the top, and two bent metal strips to hold the cups. The cups are mounted with one directly over the other so that the two ends of the loop share an axis of rotation and the loop can rotate, although only in a semicircle. All mounted on a varnished wood base with long feet on either side.

Signedengraved on base: SECRETAN / A PARIS

Curatorial RemarksFaraday's experiments on induction also used wire loops, but they would not have had to be free-moving. The fact that this loop cannot rotate more than 180 degrees suggests that it was not used for that.

FunctionAccording to Henry Noad and William Preece's Student's Text-Book of Electricity (Lockwood & co., 1867), available here, this device was developed by Ampere to demonstrate the effects of magnetic poles on electric currents. According to Noad and Preece:

"Two metallic uprights, a b, provided at their lower extremities with cups to hold mercury, are fixed on a base-board c; from the tops of these vertical rods proceed long horizontal arms, carrying at their ends brass mercury cups. The moveable conductor consists of a rectangular copper wire, its two extremities being brought back near each other, so that their points may dip into the mercury capsules, d e; one of the poles of the voltaic battery is made to communicate with the lower extremity of one of the fixed conductors, and the other with the corresponding extremity of the second pillar.

"The current will circulate through the system in a particular direction...and on placing a magnetized bar below and very near to the lower part of the wire the latter immediately moves and sets itself transversely to the magnet. On altering the direction of the current, or on turning the fixed magnet round, the wire again moves and describes an angle of 180 degrees, in order to take up a position the reverse of that which it previously occupied, and which is in strict accordance with Ampere's formula in the case of a fixed current and moveable magnet" (258).

ProvenanceDavid Wheatland purchased from Saul Moskowitz, Marblehead, Massachusetts, November 23, 1973. Donated to CHSI 1985.