Signedon scale, under black paper: ELLIOTT BROs / LONDON
Inscribedspecifications written in black marker on paper label under plastic plaque mounted on wooden black support: No 2 tangent galvanometer / one layer of 10 turns / grouped from left to right .1, .2, .2, .5 / radius of coil 18.33 cm
under black paper on scale: Use for Heavy Currents
on base: white painted MA 9
FunctionA tangent galvanometer measures the strength of an electric current. It has a circular coil with a turn of wire and a magnetic needle at the center that is either balanced on a point or suspended by a fiber of silk or quartz. The meter has to be first aligned in the north-south direction and thus the instrument takes into account the earth's magnetic field. When a current is sent through the coil, the needle is deflected according to the vector sum of the field produced by the earth and by the unknown current in the coil. The tangent of the needle's angle of deflection is proportional to the strength of the unknown current producing it.
For more information, go to the following website.
ProvenanceFrom the Department of Physics, Jefferson Lecture room, Harvard University, 02/08/1972.