Gray's "bipolar telephone" transmitter
Date: 1878
Inventory Number: 8018
Classification: Telephone
Subject:
Maker: Elisha Gray (1835 - 1901)
Owner: Jefferson Physical Laboratory, Harvard University (founded 1884)
Cultural Region:
Place of Origin:
Dimensions:
11.2 × 8.6 × 6.8 cm (4 7/16 × 3 3/8 × 2 11/16 in.)
Material:
DescriptionA bipolar telephone transmitter invented by Elisha Gray. The instrument has a flat, U-shaped metal bar, which is a permanent magnet. A hard rubber disk is attached to each pole of the magnet, which supports a diaphragm held in place by a threaded cap. The diaphragm is cushioned by rings of paper. A hard-rubber spool is inserted in each disk, attached by connecting wires. A soft-iron core screws into each pole of the permanent magnet and attached so that it may slide. It is permanently charged by the end of the magnet.
The two diaphragm assemblies are held at a 40° angle to one another, so that the lips of the center speaker, mounted between the two diaphragms, is connected to both. According to Gray's patent application, this provides two times the electro-motive force of a single diaphragm, resulting in the articulation of words with greater force and clarity.
A pair of green, cloth-covered electrical wires connects the two diaphragms and the center earphone/transmitter. An additional length of electrical wire is attached to the center of the transmitter.
Gray's patent application for his telephone was filed just a few hours after a patent application for a telephone by Alexander Graham Bell. Gray sued to have his patent primacy acknowledged, but was never successful.
Stamped on top of instrument, "ELISHA GREY / Chicago USA / X 15."
The two diaphragm assemblies are held at a 40° angle to one another, so that the lips of the center speaker, mounted between the two diaphragms, is connected to both. According to Gray's patent application, this provides two times the electro-motive force of a single diaphragm, resulting in the articulation of words with greater force and clarity.
A pair of green, cloth-covered electrical wires connects the two diaphragms and the center earphone/transmitter. An additional length of electrical wire is attached to the center of the transmitter.
Gray's patent application for his telephone was filed just a few hours after a patent application for a telephone by Alexander Graham Bell. Gray sued to have his patent primacy acknowledged, but was never successful.
Stamped on top of instrument, "ELISHA GREY / Chicago USA / X 15."
Signedon handle: ELISHA GRAY / CHICAGO. USA.
Inscribedstamped on top: ELISHA GREY / Chicago USA / X 15
FunctionDesigned to vibrate two diaphragms in front of two electro-magnets, both of which are charged from the same pole of the permanent magnet, to "secure an increased volume and clearness.."
Historical AttributesPatent application filed on March 21 1878, granted on May 21 1878 as No. 204,029.
Curatorial RemarksOld tag: "Telephone collection taken from Jeff"
ProvenanceJefferson Laboratory, Physics Department, Harvard University
Published ReferencesThis instrument is described in:
Thomas G. Hedberg, "Catalogue: Telephones, Phonographs and Related Instruments in The Collection of Historical Scientific Instruments at Harvard University." William Andrewes, Project Director (unpublished manuscript, President and Fellows of Harvard College and Thomas G. Hedberg, 1989. Fifth Draft), pp. 45-47.