Barlow's wheel

The written Barlow'sche wheel, also cal Barlow Barlow wheel or wheel, was the first Unipolarmaschine. It was created by Peter Barlow 1822.


A horizontally mounted, solid washer of highly conductive non-ferrous metals (e.g. copper or aluminum) is flooded by a axial magnetic field. The edge of the disc at the lower end immersed in a conductive liquid. In the original Barlow used mercury, for demonstration purposes, but can also consult sodium chloride solution. Similarly, galinstan, which with its physical properties comes the closest to mercury as mercury substitute is. However, aluminum and galinstan react with the addition of water exothermic, should take place in this case, the replica with copper. For longer operation of the wheel may due to oxidation to the " mudding " the Galinstans.

In a letter to Alexander Tilloch, editor of the Philosophical Magazine, writes Barlow that his bicycle had 16 spikes and consisted of thin copper sheet. For the suspension, he chose copper wire, for the gallows linkage slightly thicker copper or brass wire. About the exact measurements he gave no indication.


So that the test work, the charge carriers must pass radially through the disc. The mercury by the edge of the disk having a pole of a DC voltage source is connected. To the axis on which the disk is mounted, the other pole is created.

The charge carriers experienced by the magnetic deflection ( Lorentz force). A simple model of the movement of the carriers in metal ( electrons ) is that the motion of the electrons a " friction " counteracts (caused by collision with the atoms of the lattice) and the carrier so reach a defined speed, the drift velocity. The Barlow'sche wheel model confirms this idea by the disk begins to rotate. If there were no friction ( or a cognate force) not, the disc may not rotate. The Lorentz force acts on the basis of the orthogonality of magnetic field and electric current direction is always tangent to the wheel

An analogous experiment is the Lorentz carousel. The reverse of the phenomenon, the generation of a voltage by the rotation of a conductive plate in an axial magnetic field is known as unipolar induction.