Museo Galileo
Virtual Museum
Nobili's electromagnetic kit
    • Setting:
      Room XIII
    • Inventor:
      Leopoldo Nobili
    • Maker:
    • Date:
      ca. 1833
    • Materials:
      mahogany, boxwood, elder marrow, brass, copper, zinc, iron, steel
    • Dimensions:
      box 280x206x95 mm
    • Inventory:
    • Nobili's electromagnetic kit (Inv. 1553)

This is the fullest kit of small apparatuses to demonstrate the electromagnetic properties of current available at that time, based on the work of Hans Christian Oersted, André-Marie Ampère, Michael Faraday, Peter Barlow, Auguste De La Rive, and others. It took Leopoldo Nobili nearly nine years to develop this teaching aid. The pieces are not in the same order as those described in Nobili's Memorie (Florence, 1834), and two are missing: the box with spout for pouring mercury and the Wollaston battery. This kit, of which very few copies survive, is one of the most fascinating teaching compendia of the nineteenth century. Provenance: Lorraine collections.

The box contains:

I - FLOATING COIL (total height 65 mm). A small solenoid on top of the float of pith of elder is connected to a simple Voltaic cell of small copper and zinc plates. The solenoid will orient along the magnetic meridian when placed in acidified water. Invented by De La Rive.

II - FLOATING CIRCULAR COIL AFTER DE LA RIVE (total height 90 mm). Ring coil on a float, consisting of a few wire strands. Its orientation at right angles to the magnetic meridian is indicated by an "N" and an "S." The coil orientates along the Earth's magnetic field when placed in acidified water. Invented by De La Rive.

III - LARGE FLOATING COIL (diameter 100 mm). Large circular coil of several strands connected to a small copper plate and a small zinc plate. When suspended in acidified water, it orientates along the Earth's magnetic field.

IV - FARADAY'S CONTINOUSLY ROTATING WIRE APPARATUS (total height 68 mm). Nobili's version of Faraday's famous demonstration of 1822, in which a wire carrying a current rotates around a permanent magnet. There are three parts: a boxwood cylinder with a depression to be filled with mercury; a cylindrical magnet pushed into the center of the cylinder, with, at its top, a small cup also for mercury; a rotating conductor made of thin brass wires with a central steel pivot. Three conductors are supplied: a rectangular shape with both its limbs dipping into the mercury and two (one broken) with only one limb dipping into the mercury, and the other limb, curved upward, acting as a counterbalance. These pivoted conductors rotate around the magnet when carrying an electric current.

V - MAGNETIC CYLINDER (base diameter 32 mm). First of a series of demonstration pieces illustrating the interaction between the magnetic field of an electric current and that of a magnet, or that of another current. The turned boxwood base has a central hole for the cylindrical magnet (missing), which carried the two cups, one at the top, the other half-way down. When the cups formed a circuit with a battery, the mercury poured into them rotated in the opposite direction.

VI - MAGNETIC PEDESTAL (total height 64 mm, base diameter 32 mm). The apparatus demonstrates the interaction between the magnetic field of a current and that of a magnet. At the top of the cylindrical magnet is a depression to be filled with a drop of mercury. The drop rotates in the opposite direction to that of the mercury in the upper cup, when both are connected to an electric battery.

VI BIS - CROWN OF MAGNETIC NEEDLES (total height 69 mm, base diameter 35 mm). Series of small cylindrical magnets forming a crown, placed at the top of a boxwood pedestal. The mercury poured inside the crown will rotate under the effect of electromagnetism, when connected to a circuit that includes an electric battery.

VII - CYLINDRICAL COIL (total height 67 mm, base diameter 39 mm). Upright coil wound on a tortoise-shell cylinder with a cup-shaped depression at the top, resting on a boxwood pedestal. The end of the coil is connected to another cup mounted on a stem clamped in a brass collar. The direction of rotation of the mercury in the cup, which can be raised and lowered, is found to remain unchanged at different heights of the coil (connected to a battery).

VIII - SMALL MAGNETIC CYLINDER (total height 70 mm, base diameter 31 mm). Very thin magnet consisting of a steel bar, suspended by a silk thread for demonstrations. When the two mercury-filled cups are connected to poles of the battery the magnet will rotate on its axis. This demonstration was first performed by Ampère.

IX - APPARATUS DEMONSTRATING ELECTRODYNAMIC ATTRACTION AND REPULSION (total height 70 mm, base 71x66 mm). Wooden rectangular base with three circular depressions for mercury. The base carries a rectangular coil comprising a single wire winding on a bone or tortoise-shell support, and a brass support terminating in a cup, from which pivots a thin brass wire conductor. The pivoting wire is attracted or repelled by the coil depending on the direction of the current, as Ampère observed in his research on what were then known as "angular" currents.

X - BARLOW'S WHEEL (total height 70 mm, wheel base 76x51 mm, diameter of magnet base 32 mm). Made of two parts: a permanent horseshoe magnet, fixed in a horizontal position by a small boxwood cylinder; and a light brass wheel supported by a small fork, whose edge dips into a mercury-filled depression. When a current flows through the wheel, it will start to rotate between the magnet poles. Peter Barlow's original model of 1822 had a star-shaped wheel.

XI - FLOATING MAGNETS (height 42 mm, diameter 32 mm). A cylindrical container holds three small magnets: one in the shape of a tube weighted with a small platinum weight, the other two made up of two thin rods fixed to a platinum disk. Leopoldo Nobili showed the rotation of the magnets by electric currents by floating them in an upright position in the mercury-filled container. The cup with horizontal and vertical wires is used to demonstrate the mechanical effects of a current flowing through the mercury immersed in a magnetic field.

XI BIS - VASE WITH MAGNETIC BASE (height 71 mm, diameter 35 mm). Small cylindrical boxwood vase with upright magnetic rod terminating in a round head. To this is attached, in an upright position, one of the U-shaped magnetic needles, usually stored in the lid. Used, like item XI, to demonstrate electromagnetic rotation.

XII - SMALL BASIN WITH TWO VERTICAL WIRES (height 17 mm, diameter 39 mm). Boxwood dish with two semicircular brass cups at opposite sides, each connected to an upright wire insulated with sealing wax.

XIII - SMALL BASIN WITH TWO HORIZONTAL WIRES (height 11 mm, diameter 38 mm). Used to demonstrate the reciprocal action of current-carrying wires and magnets. When the wires form part of an electric circuit, the mercury rotates around them; this movement will be affected by a permanent magnet. The same will occur without the magnet, but much more feebly, because of the terrestrial magnetic field.

XIV - SUPPORT WITH EIGHT DIFFERENT ELECTROMAGNETIC COILS (base 123x108x60 mm). Wooden rectangular block with four pointed feet supporting eight coils of different shapes made from copper wire with burgundy-colored silk insulation. Used to demonstrate electromagnetic phenomena produced by coils.

XV - SMALL BOARD WITH THREE FLAT ELECTROMAGNETIC COILS (board 203x111 mm). Small mahogany board stained black, forming the lid of one of the compartments of the box. On the board are three flat coils: a large one in the shape of a circular crown, connected to two mercury contact-cups, one inside the crown, the other outside; and a circular and a rectangular coil, connected to three mercury contact-cups, in such a way that the middle one communicates with these two coils as well. The apparatus was used for electromagnetic experiments.

XVI - MODEL OF AMPÈRE'S THEORY OF THE MAGNETIC FIELD AROUND A CURRENT-CARRYING WIRE (length 75 mm, diameter 15 mm). Wooden rod painted black, from which emanate thin curved rods painted red and carrying small arrows. The ends of the rod are marked "N" and "S" for the magnetic poles. This model of Ampère's theory underlies all the electromagnetic phenomena demonstrated with the kit. It is a model of a wire carrying a current and behaving exactly like a magnet. The arrows at right angles indicate the circular direction of the current; the curved rods show the direction of the lines of force of the magnetic field.

XVII - BOXWOOD CONTAINER FOR MERCURY (height 65 mm, diameter 32 mm). Vessel to hold the mercury needed for floating magnets. The box also contains other items: a floating magnet consisting of two thin magnetized rods secured to a platinum disk; a cork cube with five sides covered by the same red paper as the strip glued to the inside of the box lid; and a piece of folded paper on which is written "Pomice pulv. da spargersi sul mercurio" ["Pumice powd[er] to sprinkle on the mercury"]. The sprinkled powder probably made it easier to observe the movements in the pieces of this kit.