Elihu Thomson apparatus for showing the phenomena of alternating magnetic field
Date: 1892-1896
Inventory Number: DW0089
Classification: Induction Coil
Subject:
Maker: Ducretet et Lejeune (1892 - 1896)
Inventor: Elihu Thomson (1853 - 1937)
Cultural Region:
Place of Origin:
Dimensions:
45.3 × 25.7 × 20.2 cm (17 13/16 × 10 1/8 × 7 15/16 in.)
DescriptionA primary coil of 4 1/2" around which is suspended a secondary and balanced by a cylindrical weight with a string over a large six-spoke aluminum pulley wheel housed between two bearings mounted on a brass column, all mounted on a rectangular wood base with four feet. The coil is composed of copper wires insulated by fabric covered in a black resin and wound around an iron cylinder. Over the primary coil is suspended an ebonite disc with a brass center. Suspended from the center of the disc is a loosely wound metal coil and the remnants of a glass bulb, which is hooked onto a pair of springs connected to copper contact points. Suspended by two strings from the outer edge of the disc is another coil housed in a wood ring. Two opposite points on the coil are connected to the springs above the solenoid by fabric-insulated wires.
The column housing the wheel has a knob at the bottom that raises and lowers a rubber brake on the wheel. The weight consists of three discs of varying height, each with a radial notch. The weights are suspended on a disc with a flat vertical metal shaft terminating in an eye through which is tied a string. The weights can be removed or added by lifting them up the shaft until they reach the string, which is thin enough to pass through the notches of the weights.
At one corner of the wood base are two brass binding posts with holes through their diameters at their midpoints and ridged knobs at their tops. The post on the left is connected to a switch, the one on the right to the solenoid, through wires heavily insulated. The switch connects to the solenoid. It looks similar to a telegraph key that can be held down by a clamp consisting of a T-shaped brass piece with knobs on either end. The brass piece pivots around so that one of the knobs can be positioned over the key and turned to clamp it down.
At the opposite corner of the base is a brass pillar with a steel needle at the top.
The column housing the wheel has a knob at the bottom that raises and lowers a rubber brake on the wheel. The weight consists of three discs of varying height, each with a radial notch. The weights are suspended on a disc with a flat vertical metal shaft terminating in an eye through which is tied a string. The weights can be removed or added by lifting them up the shaft until they reach the string, which is thin enough to pass through the notches of the weights.
At one corner of the wood base are two brass binding posts with holes through their diameters at their midpoints and ridged knobs at their tops. The post on the left is connected to a switch, the one on the right to the solenoid, through wires heavily insulated. The switch connects to the solenoid. It looks similar to a telegraph key that can be held down by a clamp consisting of a T-shaped brass piece with knobs on either end. The brass piece pivots around so that one of the knobs can be positioned over the key and turned to clamp it down.
At the opposite corner of the base is a brass pillar with a steel needle at the top.
Signedstamped on wheel bearing: DUCRETET & LE JEUNE / PARIS
FunctionThe arrangement is similar to an Elihu Thomson experiment in which an iron ring is made to fly away from a solenoid through the induction of a current. However, the counterweight, the wood frame around the secondary coil, and the fact that the iron core does not extend past the rod suggest that this is, in fact, not intended for that purpose.
Curatorial RemarksOriginally, the device was also labeled an "inductance coil," but the card had the term "induction coil," and this is a much more common term to use.
The wheel housing and the weights are marked D&L, but it is possible that the rest was cobbled together from other parts.
The wheel housing and the weights are marked D&L, but it is possible that the rest was cobbled together from other parts.
Primary SourcesDUCRETET, E. & LEJEUNE, L. Catalogue des instruments de précision de E. Ducretet & L. Lejeune: Troisième partie : Electricité. S.l: s.n, 1892.