Lightweight, two-wheeled, steerable machine that is propelled by the rider. The wheels are mounted in a metal frame, and the front wheel is held in a movable fork. The rider sits on a saddle and steers with handlebars attached to the fork, propelling the bicycle with two pedals attached to cranks that turn a chainwheel. An endless chain transmits power from the chainwheel to a sprocket on the back wheel. A heavy, pedalless form built in 1818 was propelled simply by the rider paddling his feet against the ground. In the early 1840s Scottish blacksmith Kirkpatrick Macmillan (1813–78) built bicycles propelled by pedals, cranks, and drive rods; he is widely credited with having invented the bicycle. Important innovations were introduced by Pierre and Ernest Michaux in France in the early 1860s, and by 1865 their company was manufacturing 400 vélocipèdes a year. A lighter version produced in England in 1870 (nicknamed the penny-farthing) featured a large front wheel and small back wheel. By the 1890s the standard bicycle design was established, and, with the smooth ride enabled by the new pneumatic tires, its popularity exploded. The so-called mountain bike became the standard design by the early 1990s. The bicycle is used worldwide as a basic means of transportation.