The bakelite ring or bobbin. 162.5 mm overall diameter wound with three coils of insulated copper wire with 2, 50 and 500 turns mounted on black bakelite moulded platform fitted with 4 terminals, rotating on a tripod non-magnetic metal base, supported by brass levelling screws. Complete with compass box(Magnetometer) mounted at the centre of the ring. Compass box(Magnetometer) spare for tangent galvonometer.
