What is the world really composed of? What is matter? Those problems really fascinated ancient scientists, especially the Greeks. If some of their conclusions seem fanciful, remember that twenty-five hundred years have passed since the Ionians began to puzzle their heads with these problems.

Heracilitus of Ephesus, Ionia (about 540-475 B.C.), held that the only reality is change, that everything is always becoming something else. He thought that fire was the principle of life -- the single element of all matter.

Heracilitus was sometimes called the "Weeping Philosopher." In his day he worried about his efforts being "obscure" and he suffered from depression.

Empedocles (about 490-435 B.C.) was born in Agrigentum, Sicily. He decided that all matter was made of four elements:

• Earth
• Air
• Fire
• Water

He said that other substances were produced by combinations of these primary elements.

One of the greatest thinkers was a man named Zeno, of Elea, Greece. He alone gave everyone else a lot to think about, with more questions than answers. One of the riddles he presented was about distance. I remember as a child being very confused about it and sore because I had to explain it before the class. To me it seemed a silly thing to spend one's time trying to figure out.

If I were to tell you that you cannot walk all the way from one side of a room to the other, reminding you of a rule that --

"Before you walk all the way across the room, you must first walk half-way," you might be puzzled and think I'm stupid.

However, if we were listening to Zeno, then the answer would be that you can never walk all the way from one side of the room to the other by this method. You walk half way. Then before you go all the remaining distance, you must go half of what is left. According to Zeno, you'll find that you can never go all the way across the room because you must always cover half the remaining distance before you cover all of it.

Now, we could prove to each other that it is impossible to travel the whole distance across the room, by using a type of reasoning based on certain problems set by Zeno, which gave philosophers and mathematicians something to ponder on for hundreds of years.

Using the method described above, Zeno "proved" that Achilles, who was a swift runner, could not catch a tortoise, even if Achilles gave the tortoise a head start.

What Zeno was really dealing with of course, was not the problem of how to catch a real tortoise, but certain puzzling mathematical questions.

Obviously, people are still having fun with Zeno, as the animation below suggests:

Aristotle (384-322 B.C.), the greatest of all the Greek scientists, was born in the far north of Greece in the little town of Stagrira.

His father was physician to the King of Macedon. The Greeks of Athens and other famous cities thought of the Macedonians as dull peasants.

They did not know that within two generations a Macedonian king, Alexander the Great, would conquer most of the known world and spread the Greek language and Greek culture wherever he went!

At this time, Athens was at the height of her glory. Plato, a pupil of Socrates, had followed his master as the greatest of Athenian philosophers.

At the age of eighteen, Aristotle made the long trip from Stagira to Athens to study at Plato''s school. Soon Aristotle became prominent in the Academy, devoting himself to science in all its branches. He became a popular lecturer.

Later, he married the adopted daughter of King Hermias, who ruled one of the tiny Green city-states, Atarneus. Aristotle lived for a while in Atarneus, then moved to Mitylene.

When he was forty-five years old, he received an invitation from King Philip of Macedon to become tutor to Philip's thirteen year old son, the headstrong Alexander.

He was Alexander's teacher for perhaps five years, until the future conqueror was eighteen. Then Aristotle returned to Athens and opened his own school, in a building called the Lyceum.

During his classes he used to walk up and down in the covered paths of the gardens, his scholars trailing along behind him as he talked. So his way of teaching came to be called Peripatetics, or walking about.

The school became famous as the place where scientists gathered to work out problems and extend the boundaries of knowledge.

Although Aristotle wrote books about astronomy, physics, politics, poetry and almost everything else, the work that modern scientists admire most is his study of animals.

He founded the science of living things, biology. He was the first to dissect fishes and insects, snakes, and octopuses scientifically. Some of his descriptions of animal structure are so accurate that they could be put into modern textbooks without change.

He was the first to study the development of creatures inside the egg (embryology) and the first to classify animals.

Working in another field, he create the science of logic. So important was his work that he was looked upon as sort of a master-mind.

For nearly two thousand years after his death, Aristotle was the supreme authority in science. This was especially true in the Middle Ages in western Europe. It took a very brave man to question any statement found in Aristotle's books.

There were attacks on Galileo for making discoveries that did not agree with Aristotle. And this was about one thousand and nine hundred years after Aristotle's death!

The curious thing is that Aristotle would have sympathized with Galileo. Like every other real scientist, Aristotle knew that sooner or later some of his theories might have to be discarded as future men discovered new facts.

Following Aristotle as had of the school in Lyceum was Theophrastus (about 372 - 287 B.C.) He was Aristotle's most brilliant pupil. He founded the science of botany.

As previously mentioned, the headstorong pupil of Aristotle's, was Alexander The Great who conquered most of the civilized world known to the Greeks. As soon as Alexander died, his generals carved kingdoms for themselves out of his empire.

Several of these Macedonian kings were lovers of literature and science. One of the, Ptolemy of Egypt, founded a sort of university, called the Museum, in Alexandria, the brilliant Egyptian city founded by Alexander and named for him.

For the next seen hundred years Alexandria was the most important scientific center in the world, scholars from far off lands coming to study in the Museum and to consult the four hundred thousand papyrus books in its library. There are so many important scientists who studied there, that it would be impossible to mention all of them.

Looking At Those Scientists Who Came After Them

One of them was Heraclides (388-312 B.C.). He was a Greek astronomer who taught that the earth turns on its axis once in twenty-four hours.

Then there was Eratosthenes (about 276 - 194 B.C.) He was the librarian of the great library, and he measured the earth and came very close to the correct figure. He was the first to suggest that men might be able to sail around the earth.

Another was Dionysius Thrax (about 100 B.C.), who made the first scientific study of the laws which govern language -- that is the subject of grammar.

Another Alexandrian Greek was named Euclid (about 330-260) B.C.). He wrote a series of textbooks that were still being used practically unchanged some two thousand years after he wrote them.

In English novels of the 19th century you frequently read that the boys had to study something called "Euclid."

What they were studying was geometry, but Euclid's fame was so great that they still referred to the subject by his name. Probably the works of Euclid have been studied more in Europe than any other book ever written, except the Bible in the past.

King Ptolemy is said to have asked Euclid if there was not a shorter way in geometry than plowing through these books.

"There is no royal road to geometry," answered Euclid. Many generations of pupils later would no doubt agree with this remark.