Maker's Name: 
W.G. Pye & Co. Ltd.
Where made: 
20 × 26.7 × 16 cm

This is an electrostatic attraction type voltmeter. The high voltage terminal is attached toan upright hollow cylinder with rounded edges. It attracts a copper plate suspended by a conducting fibre. The plate is part of a closed loop of copper moving  between the poles of a permanent magnet. This loop damps the plate movement. A beam of light is reflected off a mirror mounted on the suspension fibre, and strikes the translucent scale on the front of the instrument. Plate deflection is proportional to the square of the applied voltage which explains the nonlinear scale.