Thomson alternating ammeter
Date: 1900-1920
Inventory Number: 2002-1-0001
Classification: Ammeter
Subject:
Maker: General Electric Company (1892-present)
Cultural Region:
Place of Origin:
Dimensions:
9 x 15.5 x 14.5 cm (3 9/16 x 6 1/8 x 5 11/16 in.)
blue board box: 10.8 × 39.4 × 40 cm (4 1/4 × 15 1/2 × 15 3/4 in.)
Description:
Fan-shaped metal (brass?) case on a rectangular wood base with two binding posts and one press button. It has a window along the edge of its semicircular section, behind which is a scale. It has a range from 0 to 10 amperes, with unequal intervals between the readings. It has a reflecting band underneath the scale. A thin metal pointer hovers above the scale.
The instrument's metal parts are very rusted.
The instrument's metal parts are very rusted.
Signedbelow scale: THOMSON ALTERNATING AMMETER / NO. 36322. / PATENTED JULY 16, 1895 / GEN. ELEC. CO. U.S.A.
Inscribedon base: PROPERTY OF / HARVARD ENGINEERING SCHOOL.
on corroded metal plaque on side of instrument: HARVARD UNIVERSITY 524.
on corroded metal plaque on side of instrument: HARVARD UNIVERSITY 524.
FunctionThomson alternating ammeters were designed to measure alternating current of any frequency. The coil through which the current circulates becomes an electromagnet, attracting a strip of soft iron that moves the pointer.
For a brief description of this instrument see the "Electrical Mesurement Instruments" entry in the 1918 Encyclopedia Americana (New York: Encyclopedia Americana Corp.) Vol 10, p.318. [Available online at Google Books here.]
For a brief description of this instrument see the "Electrical Mesurement Instruments" entry in the 1918 Encyclopedia Americana (New York: Encyclopedia Americana Corp.) Vol 10, p.318. [Available online at Google Books here.]