It has been proved by actual test that the same force which draws one ton on a muddy earth road will draw four tons on a hard macadam road. One of the greatest improvements in transportation is still, in large part, neglected by the American people; and intelligent energy will find in no field richer results than in the reform of our common roads. Such a reform would economize time and force, would reduce wear and tear, and would greatly better the business position of the farmer by enabling him to choose his own time for marketing his goods and making his purchases. =345. Advantage of transportation by water; canals.=—The student may, perhaps, remember that in the Middle Ages the expense of transportation by road led people to choose rivers for conveying their goods, whenever this was practicable. It has been estimated that a horse which could carry on its back two or three centner (a centner is about 110 lbs.) could with equal exertion drag twenty centner on a highway, or 1,200 through dead-water. This enormous gain in efficiency, resulting from the avoidance of the slightest difference in level and from the reduction of force wasted in friction, suggested to people in early times the idea of establishing channels for water where none had previously existed, that is, of building canals. Locks, for controlling the flow and level of the water, were invented toward the end of the Middle Ages, and a considerable extent of canals had been constructed on the Continent before the Bridgewater canal, described above, was opened in England. The real era of the canal, however, was in the period which may be limited roughly by the dates 1750 and 1850. =346. Development of canals, 1750-1850.=—Immense amounts of capital were invested in canals in this period of their great importance; and the European and American systems of barge canals were constructed substantially on the lines which they have since retained. A traveler could then, as now, voyage through most parts of central and eastern Europe without leaving a canal-boat. Of a country like England, endowed by nature with advantages for water communication, it could be said in 1838 that no spot south of the county of Durham was more than fifteen miles from the means of water conveyance. Factories were established along the canals, as now along the railroads. Canals relieved the highways of a large part of the growing traffic, carried many raw materials which could not have borne the expense of transportation by road, and enjoyed even a considerable share of passenger traffic.