In Britain one of the mostdramatic changes of the Industrial Revolution was the harnessing of power.Until the reign of George Ⅲ(1760-1820)，available sources of power forwork and travel had not increased since the Middle Ages.There were threesources of power：animal or human muscles;the wind,operatingon sail or windmill; and running water .Only the lastof these was suited at all to the continuous operating of machines, andalthough waterpower abounded in Lancashire and Scotland and ran grain mills aswell as textile mills, it had one great disadvantage：streams flowed where natureintended them to and water-driven factories had to be located on their bankswhether or not the location was desirable for other reasons.Furthermore even the most reliable waterpower varied with the seasons and disappeared in a drought.The new age of machinery, in short, could not have been born without a new source of bothmovable and constant power.

　　The source had long been known butnot exploited.Early in the century, a pump hadcome into use in which expanding steam raised a piston in a cylinder, and atmospheric pressure brought it down again when thesteam condensed inside the cylinder to form a vacuum.This “atmospheric engine,” invented by Thomas Savery andvastly improved by his partner Thomas Newcomen,embodied revolutionary principles, but it was so slow and wasteful of fuel thatit could not be employed outside the coal mines for which it had been designed.In the 1760s, James Watt perfected a separatecondenser for the steam, so that the cylinderdid not have to be cooled at every stroke;then hedevised a way to make the piston turn a wheel and thus convert reciprocating (backand forth) motion into rotary motion.He thereby transformed an inefficientpump of limited use into a steam engine of a thousand uses.The final step camewhen steam was introduced into the cylinder to drive the piston backward as wellas forward thereby increasing the speed of the engine and cutting its fuelconsumption.

　　Watt's steam engine soon showedwhat it could do.It liberated industry from dependence on running water.The engine eliminated water in the mines by drivingefficient pumps, which made possible deeper and deeper mining.The readyavailability of coal inspired William Murdoch during the 1790s to develop thefirst new form of nighttime illumination to be discovered in a millennium and ahalf.Coal gas rivaled smoky oil lamps and flickering candles, and early in the new century, well-to-do Londoners grewaccustomed to gaslit houses and even streets.Iron manufacturers which hadstarved for fuel while depending on charcoal also benefited fromever-increasing supplies of coal; blast furnaces with steam- powered bellowsturned out more iron and steel for the new machinery.Steambecame the motive force of the Industrial Revolution as coal and iron ore werethe raw materials.

　　By 1800 more than a thousand steamengines were in use in the British Isles, and Britain retained a virtualmonopoly on steam engine production until the 1830s.Steam power did not merely spincotton and roll iron; early in the new century it also multiplied ten timesover the amount of paper that a single worker could produce in a day.At thesame time, operators of the first printing presses run by steam rather than byhand found it possible to produce a thousand pages in an hour rather thanthirty.Steam also promised to eliminate atransportation problem not fully solved by either canal boats of turnpikes.Boats could carry heavy weights, but canals could notcross hilly terrain; turnpikes could cross the hills, but the roadbeds couldnot stand up under great weights.These problems needed still another solution,and the ingredients for it lay close at hand.In some industrial regions,heavily laden wagons，with flanged wheels，were being hauled by horses alongmetal rails; and the stationary steam engine was puffing in the factory andmine.Another generation passed beforeInventors succeeded in combining these ingredients by putting the engine onwheels and the wheels on the rails, so as to provide a machine to take theplace of the horse.Thus the railroad age sprang from what had already happenedin the eighteenth century.