simple galvanometer, or galvanoscope
Date1842-1855
Inventory Number0129
ClassificationGalvanometer
Subject
Attributed to
Daniel Davis, Jr.
1813 - 1887
Cultural Region
Place of Origin
Dimensions31.8 × 28 × 12.5 cm (12 1/2 × 11 × 4 15/16 in.)
Material
Bibliography
DescriptionA bar magnet painted half white and half black pivots at its middle point so it can rotate in the horizontal plane. It is positioned within a rectangular loop of brass rods (in the vertical plane) which make three terminations at brass connectors. The latter are connected to a battery. The whole is mounted on a vertical brass post fixed on a wood stand.
This instrument allows for two options. The current may be sent through the entire rectangular loop, in which case the battery connections are made at the two cups on the same side. Or, the current may be sent only through the top or the bottom bar, in which case the battery connections are made on opposite sides of the center.
This instrument bears two old Harvard numbers: "7-95" and "6-1-6".
In 1842, Davis listed this instrument as "Galvanometer for Oersted's experiments, $3.50 to $5.00". In 1848, he sold it between $2.50 and $3.50.
This instrument allows for two options. The current may be sent through the entire rectangular loop, in which case the battery connections are made at the two cups on the same side. Or, the current may be sent only through the top or the bottom bar, in which case the battery connections are made on opposite sides of the center.
This instrument bears two old Harvard numbers: "7-95" and "6-1-6".
In 1842, Davis listed this instrument as "Galvanometer for Oersted's experiments, $3.50 to $5.00". In 1848, he sold it between $2.50 and $3.50.
Signedunsigned
Curatorial RemarksThe instrument's design dates back at least to Joseph Henry, who devised a similar demonstration apparatus in 1827. See the "Transactions of the Albany Institute", 1 (1830), 22-24. As several other instruments by Davis, this one could be from the British instrument maker F. Watkins. See also Roget's 1832 treatise on electromagnetism, fig. 59, for another example.
FunctionTo show the magnetism associated with electric current flowing in a single loop (two connections on same side) and in a straight wire (two connections are made on opposite sides).
This is how Davis explained the phenomenon in 1848: "If the wire transmitting the electrical current, after passing over the needle, is bent and returned under it, as in Fig. 53, it might be supposed that, as the electricity which flows from C to A in the upper part of the wire must pass in a contrary direction, in returning from A to B, below (the cup C being connected with the positive pole of the battery, and B with the negative), the influence of the one part of the wire would neutralize that of the other; for it has already been stated that the needle is deflected to one side or the other, according to the direction of the electrical current.
And this would in fact be the case, if the returning part of the wire were upon the same side of the needle with the other part, and at an equal distance from it. But a wire transmitting an electrical current, when passing below the needle, will produce an effect the reverse of that produced by one passing above, if the current in both cases flows in the same direction. Hence, if the direction of the electric current is reversed in the wire which passes below, it will exert a force auxiliary, and not antagonist, to that of the wire passing above. This is the case with the arrangement here represented."
This is how Davis explained the phenomenon in 1848: "If the wire transmitting the electrical current, after passing over the needle, is bent and returned under it, as in Fig. 53, it might be supposed that, as the electricity which flows from C to A in the upper part of the wire must pass in a contrary direction, in returning from A to B, below (the cup C being connected with the positive pole of the battery, and B with the negative), the influence of the one part of the wire would neutralize that of the other; for it has already been stated that the needle is deflected to one side or the other, according to the direction of the electrical current.
And this would in fact be the case, if the returning part of the wire were upon the same side of the needle with the other part, and at an equal distance from it. But a wire transmitting an electrical current, when passing below the needle, will produce an effect the reverse of that produced by one passing above, if the current in both cases flows in the same direction. Hence, if the direction of the electric current is reversed in the wire which passes below, it will exert a force auxiliary, and not antagonist, to that of the wire passing above. This is the case with the arrangement here represented."
ProvenanceFrom the Department of Physics, Harvard University.
CASIO Computer Company, Ltd.
Date: 1970-1980
Accessories: vinyl pouch with folded over snap cover and hanging loop; batteries
Object number: 1995-1-0012
Kilbourne & Clark Manufacturing Company
Date: 1922
Accessories: None
Object number: RS0059
Westinghouse Electric & Manufacturing Company
Date: circa 1918
Accessories: None
Object number: RS0058
A. H. Grebe & Company, Inc.
Date: 1920
Object number: RS0056
