Ritchie's revolving magnet
Date: 1842-1855
Inventory Number: 0108
Classification: Electromagnetic Apparatus
Maker: Daniel Davis, Jr. (1813 - 1887)
Cultural Region:
Place of Origin:
Dimensions:
26 × 11.8 × 11.8 cm (10 1/4 × 4 5/8 × 4 5/8 in.)
Bibliography:
Davis's Manual of Magnetism
A Manual of Magnetism
Daniel Davis, Jr. and the Elecromagnetic Instrument Industry: A Field with Great Potential in the Early 19th Century
Davis's Manual of Magnetism
Description:
A horseshoe-shape permanent magnet is held upright on a turned wooded base. There are two binding posts on the base. A brass rod, between the magnet's tines, supports an ivory cistern, which is partitioned into two sections. The electromagnet, which would sit on top the mercury cistern, is missing.
It has an old Harvard number: "7-3-1".
It has an old Harvard number: "7-3-1".
Signedon tines, both sides: DANIEL DAVIS JR. / MANUFACTURER / BOSTON MASS. / Price $6
FunctionAccording to Davis's 1848 book: "Instead of using a pole-changer, the poles of the electro-magnet are reversed in the following manner... The ends of the wire surrounding the revolving bar dip into mercury contained in a circular cistern of ivory, fixed between the poles of the U-magnet below the bar. This cistern is divided into two separate cells, by low partitions of ivory, so arranged that, when the electro-magnet is passing between the poles of the steel magnet, the ends of the wire may be moving across the partitions and just above them. On supplying the cells with a proper quantity of mercury, its surface will be found to curve downwards on every side towards the ivory, so that its general level will be higher than the partitions; thus allowing the extremities of the wire to be immersed in it, except when passing across them.
A wire connected with a brass cup, for making communication with the battery, projects into the mercury in each compartment of the basin. At the moment when the wires quit the mercury to pass across the partitions, a spark is seen. When the machine is put in motion in a dark room, these sparks give rise to an optical illusion of the same character as the description of the Revolving Spur-Wheel, causing the bar to appear at rest in the position it is in when the sparks are emitted." (p. 213)
A wire connected with a brass cup, for making communication with the battery, projects into the mercury in each compartment of the basin. At the moment when the wires quit the mercury to pass across the partitions, a spark is seen. When the machine is put in motion in a dark room, these sparks give rise to an optical illusion of the same character as the description of the Revolving Spur-Wheel, causing the bar to appear at rest in the position it is in when the sparks are emitted." (p. 213)
Curatorial RemarksThis instrument differs from the Page pole changer used in 0122, 0134, and 0128, which are otherwise similar instruments.
Primary SourcesDaniel Davis, Jr., Davis's Manual of Magnetism (Boston: Daniel Davis, Jr., 1842), 101-103.
Daniel Davis, Jr., A Manual of Magnetism, 2nd ed. (Boston: Daniel Davis, Jr., 1848), 213-214.
Daniel Davis, Jr., Davis's Manual of Magnetism, 7th ed. (Boston: Palmer and Hall, 1855), 213-214.
Daniel Davis, Jr., A Manual of Magnetism, 2nd ed. (Boston: Daniel Davis, Jr., 1848), 213-214.
Daniel Davis, Jr., Davis's Manual of Magnetism, 7th ed. (Boston: Palmer and Hall, 1855), 213-214.
ProvenanceFrom the Department of Physics, Harvard University.