The Mine Safety Appliances Company Ltd. manufactured this type W-8 methanometer around 1950. It was used to detect how much methane gas was present in the air and was approved for use by the Ventilation Regulations of 1947.
The methanometer could be powered by an Edison battery cap lamp and would be carried on a miner's belt with other tools.
Methane is the main gas present in 'firedamp'. It is highly explosive and had previously been detected by the blue halo effect it gave to the flame of a safety lamp.