religion rather than scientific investigation to answer their questions about the laws of nature. At the same time Arabic scholars were correcting Ptolemy system of astronomy and performing experiments in optics and mechanics. As trade increased between Arab countries and western countries, their work and Greek scientific documents became available to western culture. During the 1200's St. Thomas Aquinas reconciled Aristotle's beliefs with church principles. During this time Roger Bacon an English scholar conducted studies in optics. During the Renaissance there were many social, economic and political changes that produced new approaches to science. The famous Italian painter Leonardo da Vinci conducted studies in motion and hydraulics. The polish astronomer Nicolaus Copernicus proposed a system in which the sun was placed at the centre of the universe and the earth was one of the planets orbiting the sun. Gerhard Herzberg received a Nobel Prize for his studies of the ways atoms and molecules give off and absorb light. The Alouette satellites, which were launched in the 1960s, have helped Physicists to study matter high above the earth's surface. At the turn of the twentieth century the understanding of the physical universe changed completely when Antoine Henri Becquerel and Wilhelm Roentgen discovered radioactivity and x-rays. A general, theoretical picture for the generation of x-rays emerged after Niels Bohr developed the first atomic theory. ...
