After a while steam engines began to pull trains over rails and drive ships through the water. They ran threshing machines on farms. Then inventors used their new knowledge about power to make other kinds of engines driven by gasoline or electricity or oil. [Illustration] At last some of this new machinery began to work its way back into the mines. Power driven elevators carried the men up and down shafts to their work. But the miners still did all the coal digging and loading by hand. Today many miners use power-driven drills for digging. Mechanical loaders pick up the loose coal and put it into small cars on the tracks in the tunnel. A little electric locomotive pulls the cars away to the elevator which hoists them up above ground. The most remarkable digger of all is the one you’ll see on the next page. It rolls along a track deep underground until it comes to the place where its operator wants to cut coal. He pushes a control, and the machine’s long neck reaches up. The cutting head, at the end of the neck, starts biting into the coal. The head does its work much faster and easier than men with hand tools ever could. [Illustration] Outside the mine, machines sort the coal according to size and load it into railroad cars. [Illustration] Unloading machinery empties the cars in many places, too. There’s one coal yard where a woman, pushing buttons, controls machines that do everything--unload cars, store the coal according to its size in tall bins, and load the trucks that will deliver it to customers. This is how the yard works: Each railroad car empties its coal in a stream onto a moving belt. The belt carries the coal to a machine called a giraffe, which works like an escalator. The giraffe lifts the coal into a tall hopper. [Illustration] The woman who runs the coal yard sits in an office with a big window, where she can look out and see everything that’s going on. When a truck has backed up to a hopper, ready to load, she pushes a button. Coal drops down out of the hopper onto another giraffe which lifts it into the body of the truck. As soon as the truck is filled, push goes a button and the loading stops. LOADERS, LIFTERS AND SUCH Moving belt machines work at other jobs, too. They load sand into trucks and cargo into ships. On some piers, huge vacuum cleaners empty ships full of sugar or wheat. At ports on the Great Lakes, machines reach down into ore-carrying ships and unload them with great speed. At the end of each of these unloaders hangs a clamshell bucket. Just above the bucket is a little room where a man sits and watches what goes on. He signals to the operator, telling him just where to drop the bucket so it can pick up a mouthful of ore. The ship can be unloaded by two men who do nothing but signal to each other and push levers. But usually there are several machines working at the same time so that the job goes as quickly as possible.