John Davis first started to produce the Biram anemometer in Derby, in 1845. The anemometer was an instrument designed to measure the flow or velocity of air and was used in the ventilation of mine shafts.
The anemometer's metal frame contains a brass propeller. The propeller is attached to a dial that records the number of turns that it makes and converts this reading into a measurement of air speed.
In deep coal mines, the gases given off by the coal can accumulate in the mine passages and become concentrated. When this happens, the slightest spark can set off an explosion. To prevent this happening, big fans are used at the pit top to draw fresh air around the mine and take the gas away to the surface. Anemometers were used by the Mine Deputies every day to check that there was a sufficient flow of fresh air throughout the whole mine.