Humans have always been very curios creatures. The have always wondered about what they are and why they are here. Our limited knowledge of the environment has always urged for new things to be discovered. The desire to understand the world better has made people search for rational answers, for principles and laws. For centuries people have tried to unlock the mysterious world that surrounds them.
             Because myths did not explain things well enough the Greeks began to ask questions about the world around them. They did this so thoroughly and so brilliantly that the era between 600 and 400 B.C. is called the golden age of philosophy. The Greek philosophy was an attempt to find the truth about unexplained phenomena, mostly by trying to think things through, not by running experiments in a laboratory. The philosophers wanted to discover the basic nature of things and some of them believed that they could find one thing that everything else was made of. A philosopher named Thales said that this substance was water, but another named Anaximenes thought it was air. A third called Empedocles said that the world was composed of four elements: earth, air fire and water.
             Aristotle became the most influential of the Greek philosophers, and his ideas dominated science for nearly two millennia after his death in 323 BC. He believed that four qualities were found in nature: heat, cold, moisture, and dryness. The four elements were each composed of pairs of these qualities; for example, fire was hot and dry, water was cold and moist, air was hot and moist, and earth was cold and dry. These elements with their qualities combined in various proportions to form the components of the earthly planet. Because it was possible for the amounts of each quality in an element to be changed, the elements could be changed into one another; thus, it was thought possible also to change the material substances that were built up from the elements-lead into gold, fo...