The basic galvanometer, devised by the British physicist
William Sturgeon (1783-1850) in 1825, allows all of the various combinations
of current and magnetic needle direction to be tried out. By making suitable
connections to the screw terminals, current can flow to the right or to
the left, both above and below the needle. Current can be made to travel
in a loop to double the effect, and, with the aid of two identical external
galvanic circuits, the currents in the two wires can be made parallel and
in the same direction. Note that the wires are insulated from each other
where they cross. From a pedagogical point of view, it would be better
if the pivoted magnet were smaller, since we usually talk about the magnetic
field at a point rather than the average magnetic field over a region.
I often the apparatus at the top when starting the discussion of the magnetic
fields set up by steady currents, and, with a certain amount of feigned
confusions, can get the students to “explain” the situation to me.
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