There was with Watt and his contemporaries apparently a fondness for cost and complications. Most likely the finished Watt engine was a handsome and stately machine, imposing in its deliberate movements. There is apparently nothing simpler than the placing of the head of the piston-rod between two guide-pieces to keep it in line and give it bearing. Yet we have only to turn back a few years and see the elaborate and beautiful geometrical diagram contrived by Watt to produce the same simple effect, and known as a "parallel motion." It kept its place until the walking-beam was cast away, and the American horizontal engine came into almost universal use. The object of this chapter so far has been to present an idea of beginnings; of the evolution of the universal and indispensable machine of civilization. The steam-engine has given a new impetus to industry, and in a sense an added meaning to life. It has made possible most that was ever dreamed of material greatness. It has altered the destiny of this nation, and other nations, made greatness out of crude beginnings, wealth out of poverty, prosperity upon thousands of square miles of uninhabitable wilderness. It was the chiefest instrumentality in the widening of civilization, the bringing together of alien peoples, the dissemination of ideas. Electricity may carry the idea; steam carries the man with the idea. The crude misconceptions of old times existed naturally before its time, and have largely vanished since it came. Marco Polo and Mandeville and their kind are no longer possibilities. Applied to transportation, locomotion alone, its effects have been revolutionary. Applied to common life in its minute ramifications these effects could not have been believed or foretold, and are incredible. The thought might be followed indefinitely, and it is almost impossible to compare the world as we know it with the world of our immediate ancestors. Only by means of contrasts, startling in their details, can we arrive at an adequate estimate, even as a moral farce, of the power of steam as embodied in the modern engine in a thousand forms. * * * * * Perhaps it might be well to attempt to convey, for the benefit of the youngest reader, an idea of the actual working of the machine we call a steam-engine. There are hundreds of forms, and yet they are all alike in essentials. To know the principle of one is to know that of all. There is probably not an engine in the world in effective common use--the odd and unusual rotary and other forms never having been practical engines--that is not constructed upon the plan of the cylinder and piston. These two parts make the engine. If they are understood only differences in construction and detail remain.