Maker's Name: 
Telegraph Works Silvertown London
Where made: 
circa 1910?
9 × 6 × 11 cm

This form of galvanometer, also known as a ‘Q and I detector’, was used as the basic diagnostic tool by telegraph linemen.  A horizontal axle carries an indicator in front of the dial and a magnetised needle inside, located between two coils. Two inclined bar magnets helped maintain the magnetisation of the needle.  The higher resistance coil was connected to indicate voltage  (‘Intensity’)and the lower resistance coil was used to indicate current (‘Quantity’).