You could do everything that the machines in this book do. For some of the jobs, of course, you’d have to get friends to help you. But people have always been able to work and build wonderful things, using just their muscles. And they can do a very great deal more when they use their brains, too. They can invent machines to make work thousands of times easier and faster.

The big machine in the picture is a shovel that’s used for digging an enormous hole. In one bite, its scoop can tear out a chunk of earth more than twice as tall as a man. Its long arm, called the boom, lifts the load as high as the top of a seven story building, then swings around and drops it almost a city block away.

There are only a few shovels like this in the world. They were especially made to work where beds of coal lie close to the surface of the earth, covered by a layer of soil. The shovels clear away the soil so that other machines can dig out the coal.

When a giant shovel has cleared off one spot, its crawlers begin to turn, and it creeps slowly ahead. But it can’t travel on roads. It’s far too big and heavy and tall—so big, in fact, that it came to the mine in separate pieces. Forty-five freight cars were needed to haul all the parts for just one machine from the factory to the mine. Then experts put the parts together right where the shovel was to start digging.

And dig it does. In one minute its scoop can bite out as much dirt as 3,600 men could dig just using their muscles to lift ordinary hand shovels!

The giant shovel is one of the biggest machines ever made, but there’s another that can lift even bulkier things. It is an overhead crane that works in a shipyard.

Often the crane hoists big boilers out of ships so that repair men can work on them. It is so huge that it carries another crane on its back. The piggy-back crane—that’s its real name—reaches down and lifts things off the deck of the ship, too.

Hammering is another kind of muscle work that

machines can do quickly and easily. Suppose the water pipes under your street need mending. Repair men have to tear up the pavement in order to reach the pipes. So they bring in jack hammers to do the pounding. Strong blasts of air run the hammers, and, in no time, the pavement is broken up.

Crushed rock was used for making the paved street in the first place. It came from a big machine called a rock crusher, which breaks up chunks of stone into small pieces. Strong jaws inside the crusher chew at the stone until they have made it into bits that are just the right size.

An even bigger pounding machine is the pile driver. It can hammer a great thick log down into the ground almost as easily as a man can hammer a nail through a board. One kind of pile driver does its pounding job with a steam piston. Another kind lifts a heavy weight and lets it bang down on top of the log, called a pile. The one in the picture works in a harbor. It drives piles deep into the earth that lies under water. A whole group of piles make the foundation for a pier in the harbor, for ships to tie up alongside.

Harbors and rivers must be kept safe for ships. If mud and sand pile up in a thick layer on the bottom, ships may get stuck. So dredges go to work clearing the mud and sand away. Often a clean-up job takes a long time. The men who run the machinery live on board the dredge, just as sailors live on a ship.

Some dredges have scoops that dig under water. Others, like the one in the picture, use giant suction pumps. The mud or sand they suck up is called spoil.

If there’s hard-caked mud on the bottom, cutter heads break it up. Then it’s ready to be pumped out through huge steel pipes that stretch away from the dredge like a great snake and pour the spoil out on land.

Of course, a dredge must stay in one place while it is working. So it carries along two huge spikes called spuds. These move straight up and down at the stern of the dredge. When they ram into the earth underwater, they keep the dredge from drifting.

A spud is so heavy that it pokes its own hole in the muddy bottom of a river or harbor. But making holes on dry land is a different problem. For instance, you can’t just poke a telephone pole into the hard ground, or pound it in easily with a pile driver, either. So, in many places, a machine bores holes for telephone poles, just the way a carpenter bores a hole with a brace and bit. Then the machine’s long arms reach out, lift a pole into the air and plug it down neatly into place.

Long ago our ancestors discovered how to use simple tools—such as hammers, shovels, crowbars and rollers. These things seem very ordinary to us, but they were really wonderful discoveries. The clever men who invented them were providing ideas, one by one, which scientists and engineers used much later. Our great machines are combinations of many, many things that men discovered from using simple tools.