ballistic galvanometer with moving magnet
Date: 1900-1910
Inventory Number: 0229a,b,c,d
Classification: Galvanometer
Subject:
Maker: Nalder Brothers & Company (founded 1884)
User: Department of Physics, Harvard University (founded 1884)
Cultural Region:
Place of Origin:
City of Use:
Dimensions:
26.2 × 18.7 × 21 cm (10 5/16 × 7 3/8 × 8 1/4 in.)
Description:
Galvanometer with bell-shaped moving magnet on an aluminum wire with small mirror and weights. Coils mounted in hinged ebonite case that swings open. Coil case is attached to two ebonite supports. Round hard rubber tripod base with three leveling screws and one binding post. Cylindrical brass case with viewing window fits over galvanometer. Two terminals protrude through case sides.
The instrument is marked with a painted blue triangle, which indicates it was used in the Physics 3 course at Harvard in the late 1920's.
The instrument is marked with a painted blue triangle, which indicates it was used in the Physics 3 course at Harvard in the late 1920's.
Signedon top of case: NALDER BROs & Co / LONDON / No 3466
FunctionThe ballistic type galvanometer is a moving coil galvanometer that measures electric charge, but its coil is specially designed with less torque and higher inertia and its mirror is deflected in a way that is proportional to the total charge passing through the moving coil.
Curatorial RemarksAccording to the card, this instrument was designed by Nalder Brothers. This instrument is a "special form of ballistic galvanometer designed by Messrs. Nalder Bros...; in it the magnets, which are bell-shaped to diminish air friction, are arranged astatically, two being in the center of the coil and two being outside, one above and one below the coil. The coils which are hinged to give easy access to the needle, are mounted in ebonite cases, and the whole highly insulated; there is as little solid metal as possible in the vicinity of the needles, as eddy currents might be set up, which would increase the damping action. The mirror is also reduced in size as much as possible, on account of air friction." From Henderson, Practical Electricity and Magnetism (London, 1908),vol II, p. 247-8, fig. 104.
ProvenanceFrom the Department of Physics, Harvard University, 12/18/1956.