Device for developing conical ducts

Used for determining the speed of wind (or of water), this instrument was made up of two conical ducts whose bases have an area ratio of 1 to 5. Opposite them was a blade turbine rotating about an axle, around which coiled a rope supporting a weight for determining the force of wind. The twin ducts are for testing the measuring capacity of the device. The proportion between the two measurements, in effect, had to be 1 to 5, exactly like the ratio between the ducts' areas.
Codex Arundel, sheet 241