double unit string oscillograph, type 338-DO
Date: 1928-1932
Inventory Number: RS0613
Classification: Oscillograph
Subject:
Maker: General Radio Company (1915-present)
User: Cruft Laboratory, Harvard University ? (founded 1914)
Cultural Region:
Place of Origin:
City of Use:
Dimensions:
35.3 x 62 x 20.5 cm (13 7/8 x 24 7/16 x 8 1/16 in.)
Accessories: 3 bulbs; small vial with oil; 7 rectangular pieces with 2 dials and brackets (all in drawer)
DescriptionThe double string oscillograph is a black instrument with a square base, described in further detail below. It is mounted on one end of a rectangular wooden cabinet. At the opposite end of the cabinet there is one drawer (containing several accessories), and mounted on top a tall rectangular box that contains a mirror mechanism used to observe the readings from the string oscillograph. The cabinet itself has four binding posts, a dial and a switch.
The double string oscillograph itself is composed of two identical string oscillographs, mounted alongside with the same orientation so that they can be read simultaneously. Also mounted on the instrument's base are two identical potentiometers to regulate the amount of electricity passing through the wires, and four binding posts (two for each wire oscillograph).
Each of the oscillographs is made of a pair of U-shaped permanent magnets, amidst the poles of which is an electrical mechanism including a thin metal wire. A horizontal cylindrical cavity traverses the system and would contain several optical elements to illuminate the string and project its shadow out towards one side.
A lamp would be mounted at the end of the pair of oscillographs to illuminate the wires, casting their shadows. In use, the instrument would be oriented so that the light coming out of the cavity (with the shadows) was directed into the mirror mechanism at the opposite side of the wooden cabinet.
The cabinet drawer contains several brackets and electrical parts, a bulb for the (missing) lamp, and a small glass bottle of oil with cork cap and dropper, for damping the movement of the wires if desired.
The double string oscillograph itself is composed of two identical string oscillographs, mounted alongside with the same orientation so that they can be read simultaneously. Also mounted on the instrument's base are two identical potentiometers to regulate the amount of electricity passing through the wires, and four binding posts (two for each wire oscillograph).
Each of the oscillographs is made of a pair of U-shaped permanent magnets, amidst the poles of which is an electrical mechanism including a thin metal wire. A horizontal cylindrical cavity traverses the system and would contain several optical elements to illuminate the string and project its shadow out towards one side.
A lamp would be mounted at the end of the pair of oscillographs to illuminate the wires, casting their shadows. In use, the instrument would be oriented so that the light coming out of the cavity (with the shadows) was directed into the mirror mechanism at the opposite side of the wooden cabinet.
The cabinet drawer contains several brackets and electrical parts, a bulb for the (missing) lamp, and a small glass bottle of oil with cork cap and dropper, for damping the movement of the wires if desired.
Signedetched and white filled on top panel: DOUBLE UNIT / STRING OSCILLOGRAPH / TYPE 338- DO SERIAL NO. 12 / GENERAL RADIO CO. / CAMBRIDGE, MASS.
raised lettering on dials: GENERAL RADIO CO. / CAMBRIDGE, MASS.
raised lettering on dials: GENERAL RADIO CO. / CAMBRIDGE, MASS.
FunctionString oscillographs were devices used to visualize rapidly varying electric currents or voltages, and were the direct predecessors of the cathode-ray oscilloscope. They worked by converting the signal into vibrations on a thin string. Early string oscillographs would have a mirror or other elements mounted on the wire to reflect light off.
Later examples, such as this one, were meant to be much more sensitive by using much thinner wires. Instead of having some element mounted on the wire, these devices visualized the electric signal by projecting the shadow of the wire as it moves in response to the signal.
In this particular instrument, two such oscillographs have been mounted one after the other, so that the resulting reading can contain two independent signals at once.
In order to convert the left-right movement of the shadow(s) into a more visual, graph-like image, this oscillograph comes with a mechanism consisting of an octagonal metallic mirror that is turned by a motor at speeds that the user can regulate. This displaces the position of the shadows in a direction perpendicular to the wire movement at periodic intervals.
Later on, General Radio also offered a camera system to instead record the up-and-down movement on rolling photographic film.
The string oscillograph became less popular in the early 1930s with the implementation of the sweep circuit, which made the cathode ray tube oscillograph a much easier way to visualize electric signals than was the use of rotating mirrors or cameras.
Later examples, such as this one, were meant to be much more sensitive by using much thinner wires. Instead of having some element mounted on the wire, these devices visualized the electric signal by projecting the shadow of the wire as it moves in response to the signal.
In this particular instrument, two such oscillographs have been mounted one after the other, so that the resulting reading can contain two independent signals at once.
In order to convert the left-right movement of the shadow(s) into a more visual, graph-like image, this oscillograph comes with a mechanism consisting of an octagonal metallic mirror that is turned by a motor at speeds that the user can regulate. This displaces the position of the shadows in a direction perpendicular to the wire movement at periodic intervals.
Later on, General Radio also offered a camera system to instead record the up-and-down movement on rolling photographic film.
The string oscillograph became less popular in the early 1930s with the implementation of the sweep circuit, which made the cathode ray tube oscillograph a much easier way to visualize electric signals than was the use of rotating mirrors or cameras.
Curatorial RemarksFor single version of this instrument, which also includes a lamp, see RS0359.
Primary SourcesThe single version of this string oscillograph, including the rotating mirror arrangement, is described in:
Charles L. Reutz, Modern Radio Reception (New York, 1928), pp. 71-74. Available on Google Books here.
The photographic recording system for this oscillograph is described in:
Horatio W. Lamson, "A Continuous-Film Camera for the Oscillograph". The General Radio Experimenter, Vol. V. No. 11 (April 1931). Available online here.
Charles L. Reutz, Modern Radio Reception (New York, 1928), pp. 71-74. Available on Google Books here.
The photographic recording system for this oscillograph is described in:
Horatio W. Lamson, "A Continuous-Film Camera for the Oscillograph". The General Radio Experimenter, Vol. V. No. 11 (April 1931). Available online here.
ProvenanceMarked as possibly from the Cruft Laboratory, Harvard University.
