EXHIBITS > Measuring instruments, tools and machines of the ancient Greeks >
Road counter ''Odometre''
Mechanism for accurate measurement of road distance (precursor of the taximetre). It consisted of a box with co-operating screws and gearwheels attached to a moving vehicle. One axial rod on one of the vehicle’s wheels carried the motion to the first eight-toothed (gear)wheel in the box, while the calibrated discs on the outer top surface of the box which were embedded on the axles indicated the distance travelled. The ratio in the proposed Heron’s construction is 1:8:30:30:30 so a full rotation of the last disc corresponded to 216000 revolutions of the vehicle’s wheels. By the wheels’ diametre of 1.60 metres the distance is 1080 kilometres.
In a variation of the device one calibrated disc had radial holes with balls that when one of them was aligned with a corresponding hole of the box the ball fell into a metal vessel offering easy measurement of the distance. Archimedes is probably the inventor of this device. (Jejis Ioanis, Thousands 2, 12th century. A.D.)
SOURCES: "Vitruvius, On architecture, X 9", "Heron of Alexandria, On dioptra"