We have now traced the steps by which man mastered the art of kindling a fire quickly and easily and have followed the progress that has been made in the most common uses of fire. But the story of a most important use of fire remains to be told, the story of its use in doing man's _work_. How important this use is, how much of the world's work is done through the agency of fire, a little reflection will make plain. Fire makes steam and what does steam do? Its services are so many you could hardly name all of them. The great and many services of steam are made possible by the fire-engine, or _steam-engine_, and the story of this wonderful invention will now be told. That steam has the power to move things must have been learned almost as soon as fire was used to boil water. Heat water until it boils and the steam that is formed is bound to move something unless it is allowed to escape freely. It will burst the vessel if an outlet is not provided. That is why a spout has been placed on the tea-kettle. Where there is cooking, steam is abundant and the first experiments in steam were doubtless made in the kitchen (Fig. 1). It has been said that the idea of the steam-engine first occurred to Adam as he watched his wife's kettle boil. [Illustration: FIG. 1.--FIRST EXPERIMENTS WITH STEAM.] Whatever may have happened in ancient kitchens, we are certain that there were no steam-engines until many centuries after Adam. The beginnings of this invention are not shrouded in so much mystery as are those of the match and the lamp and the forge. In giving an account of the steam-engine we can mention names and give dates from the very beginning of the story. We know what the first steam-engine was like and we know who made it and when and where it was made. It was made 120 B. C. by Hero, a philosopher of Alexandria in Egypt. It was like the one shown in Figure 2. The boy applies the fire to the steam-tight vessel _p_ and when steam is formed it passes up through the tube _o_ and enters the globe which turns easily on the pivots. The steam, when it has filled the globe, rushes out of the short tubes _w_ and _z_ projecting from opposite sides of the globe and bent at the end in opposite directions. As it rushes out of the tubes the steam strikes against the air and the reaction causes the globe to revolve, just as in yards we sometimes see jets of water causing bent tubes to revolve. This was Hero's engine, the first steam-engine ever made. [Illustration: FIG. 2.--HERO'S ENGINE, 120 B. C.]