<text><span class="style10">ngines (1 of 5)</span><span class="style7">The tempo of human life, the jobs we do, and the structure of society itself were all transformed by the invention of heat engines - engines that use energy provided by heat to do work. The steam engine, invented in the 18th century, greatly extended mass production in factories, as well as providing power for railways and ships. The internal-combustion engine, invented at the end of the 19th century, greatly increased personal mobility through the motorcar. And the jet engine, the 20th century's contribution, has made travel to the ends of the Earth an everyday occurrence. Before the invention of heat engines, man depended on animals to draw the plow and provide transport, and on waterwheels and windmills to supply power for industry. But even the biggest mills generated no more than 10 horsepower - about 7 kilowatts.</span></text>
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<text><span class="style10">he Double-Acting Steam Engine</span><span class="style7">The principal component of a typical Watt double-acting steam engine, as built c. 1790. Steam from a boiler was introduced alternately on either side of the piston, so that the engine was ΓÇ£double-actingΓÇ¥ - both the upstroke and the downstroke were powered by steam. After passing through the cylinder, the steam was condensed to water, which was extracted by means of an air pump. As the steam condensed, a partial vacuum was created in the part of the cylinder into which the piston was moving. Thus - although the steam pressure in WattΓÇÖs engine did not exceed 1_ atmospheres - the relative pressure difference within the cylinder increased the effective power of the engine.</span></text>
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<text>ΓÇó SPACE EXPLORATIONΓÇó THERMODYNAMICSΓÇó TRANSPORTATIONΓÇó THE INDUSTRIAL REVOLUTION</text>
