Signedunsigned
FunctionFor instructional demonstration of the induction of electricity in coiled wires when the coil is rapidly turned in the presence of Earth's magnetism.
This is how Davis described the experiment in 1848: "Stronger deflections are produced by causing a helix [coil] to revolve rapidly, as in the instrument represented in Fig. 184. The coil which is hollow, moves in a vertical plane, and its shaft is provided with a pole-changer, to the segments of which the extremities of the wire are soldered. The springs pressing on these segments convey the currents to the screw-cups on the base board. When the cups are connected with those of a delicate galvanometer, and the instrument placed in such a direction that the helix shall move in the magnetic meridian, it is made to revolve rapidly by means of a multiplying wheel. As each end of the helix approaches and recedes from the line of the dip, opposite currents are induced in the wire, their direction changing as the helix passes this point." (pp. 306-307)
Primary SourcesDaniel Davis, Jr., Catalogue of Apparatus, to Illustrate Magnetism, Galvanism, Electrodynamics, Electro-Magnetism, Magneto-Electricity, and Thermo-Electricity (Boston: Daniel Davis, Jr., 1848), 39, fig. 184.
Daniel Davis, Jr., A Manual of Magnetism, 2nd ed. (Boston: Daniel Davis, Jr., 1848), 306-308.
Daniel Davis, Jr., Davis's Manual of Magnetism, 7th ed. (Boston: Palmer and Hall, 1855), 306-308.
ProvenanceFrom the Department of Physics, Harvard University.
Related WorksSara Schechner, "Daniel Davis, Jr. and the Electromagnetic Instrument Industry: A Field with Great Potential in the Early 19th Century," unpublished manuscript (1978), available in the CHSI Library (Lib.4884).