Before the development of a gear system to multiply the revolutions of the pedals, these were linked directly to the wheel. Thus to increase the maximum speed, the driven wheel at the front was enlarged. The position of the rider was moved so he was sat directly above the wheel, so it could be enlarged to its maximum limit, given by the length of the rider's legs.
This meant that the rider's feet could not reach the ground while riding, and the penny-farthing was notorious for causing accidents. It is effectively little more than a unicycle with an extra wheel for stability.
By the 1890s, the modern bicycle (known originally as the Safety bicycle due to its great safety improvements over the penny-farthing) had become established, and penny-farthings are nowadays only museum pieces or kept by hobbyists.