ID: 
47
Maker's Name: 
Cambridge instrument Co. Ltd., England
Where made: 
England
Dimensions: 
20 × 20 × 32 cm

An electrostatic voltmeter following a design by Ayrton and Mather. A beam of light reflected by a mirror acts as the 'needle'.

It could measure DC or AC voltges up to about 10V. It had extremely high impedance but a slow response time measured in seconds.

Details are available in the CIC catalogue entry below.